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User:Jianing Song

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You don't try to extend these sequences: A000679, A094268, A257479.

Some really fast-growing functions in the OEIS: A056041/A266203 (the weak Goodstein function, growth ω), A154714 ({fn(2)}, growth ω), A188545 (the "fuse" function, growth ε0), A028444/A060843 (the "BB" function, growth ω1CK).

Note that fuse(3)>2↑↑↑↑↑↑↑↑↑16, and BB(6)>2⇈2⇈222222226 (see here).

The most interesting sequences in my eyes: A046073, A105876, A298821.

The sequences I submitted myself that I'm most satisfied with: A306198, A400743.

Theta series for some best-known lattices

Name Description Theta series {a(n)} {a(n)/a(1)}
Square ℤ[i] A004018 A002654
Hexagonal, A2 ℤ[ω] A004016 A002324
Cubic ℤ3 A005875 -
4D cubic ℤ4 A000118 A046897
D4 ℤ4∪(ℤ+12)4 A004011 A000593

Examples of factorizations

For G a subgroup of Gal⁡(L/K), we write LG to be the fixed field of G. We consider L/K=ℚ(ζ24)/ℚ, with Galois group (ℤ/24ℤ)×.

Fixed field Field Discriminant ℚ2⊗... (2)⊂ℤ ℚ3⊗... (3)⊂ℤ
ℚ(ζ24){1,5} ℚ(i,6) 2304 ℚ2(i,6) 𝔭24 ℚ3(ζ12) 𝔭32
ℚ(ζ24){1,7} ℚ(2,−3) 576 ℚ2(2,−3) 𝔭22 ℚ3(ζ12) 𝔭32
ℚ(ζ24){1,11} ℚ(−2,3) 2304 ℚ2(−2,3) 𝔭24 ℚ3(3)2 𝔭32𝔭'32
ℚ(ζ24){1,13} ℚ(ζ12) 144 ℚ2(ζ12) 𝔭22 ℚ3(ζ12) 𝔭32
ℚ(ζ24){1,17} ℚ(ζ8) 256 ℚ2(ζ8) 𝔭24 ℚ3(i)2 𝔭3𝔭'3
ℚ(ζ24){1,19} ℚ(−2,−3) 576 ℚ2(−2,−3) 𝔭22 ℚ3(−3)2 𝔭32𝔭'32
ℚ(ζ24){1,23} ℚ(2,3) 2304 ℚ2(2,3) 𝔭24 ℚ3(ζ12) 𝔭32

Chebyshev's bias

Subgroup Coset Primes Coset Primes Coset Primes
{1,5} {7,11} {13,17} {19,23}
{1,7} {5,11} {13,19} {17,23}
{1,11} {5,7} {13,23} {17,19}
{1,13} {5,17} -1: A297354/A297355 {7,19} -1: A297356/A297357
0: A380877
{11,23} very large
{1,17} {11,19} very large {5,13} -1: A297447/A297448
0: A379989
differences: A379731
{7,23} -1: A295353/A295354
{1,19} {5,23} -1: A398234 {7,13} -1: A398235 {11,17} -1: A398236
{1,23} {5,19} {7,17} {11,13}

The world of nuclides is full of mysteries

Unknown decays: 48Ca (β−), 123Te (β+), 149Sm (α), 180mTa (β+/β−/IT), 187Os (α), 222Fr (α), 247Cm (β−), 248Bk (α/β+/β−);

Unknown if decay is energetically possible: β− of 222Rn.

Bound-state β− decays

By conservation of energy, we have Qβ−(ZAXn+)=Qβ−(ZAX)+∑i=1nIi(Z)−∑i=1nIi(Z+1), where Ii(Z) and Ii(Z+1) are respectively the i-th ionization energy of element X and the next element.

Write E(Z)=∑i=1ZIi(Z) be the total binding energies of electrons, then

Qβ−(ZAX(Z−n)+)=Qβ−(ZAX)+(E(Z)−∑i=1nIZ+1−i(Z))−(E(Z+1)−∑i=1n+1IZ+2−i(Z+1))=Qβ−(ZAX)−(E(Z+1)−E(Z))+∑i=1n(IZ+2−i(Z+1)−IZ+1−i(Z))+IZ+1−n(Z+1).

In particular, for n=0,1, we have Qβ−(ZAX(Z−n)+)≈Qβ−(ZAX)−(E(Z+1)−E(Z))+IZ+1(Z+1);

for n=2,⋯,9, we have Qβ−(ZAX(Z−n)+)≈Qβ−(ZAX)−(E(Z+1)−E(Z))+IZ−1(Z+1).

First category: Qβ−<0 for neutral atoms

Data from NIST (please beware that these are most predictions). All values are in unit of keV.

Beta decay Qβ−(ZAX) E(Z+1)−E(Z) IZ+1(Z+1) Qβ−(ZAXZ+) ∑i=12(IZ+2−i(Z+1)−IZ+1−i(Z))+IZ−1(Z+1) Qβ−(ZAX(Z−2)+)
148Eu → 148Gd -28 ± 10 11.6 59.06554 19 18.08746 -22
163Dy → 163Ho -2.831 ± 0.022 12.5 65.13713 49.806 19.84548 4.514
193Ir → 193Pt -56.63 ± 0.30 15.9 90.65984 18.13 27.2647 -45.27
194Au → 194Hg -28 ± 4 16.8 95.89819 51 28.7966 -16
202Tl → 202Pb -40 ± 4 17.3 101.3367 44 30.3914 -27
205Tl → 205Pb -50.6 ± 0.5 17.3 101.3367 33.4 30.3914 -37.5
213Po → 213At -74 ± 5 18.4 109.8872 17 32.9085 -59
215At → 215Rn -88 ± 9 18.7 112.8422 6 33.7745 -73
222Rn → 222Fr -6 ± 8 19.2 115.8575 91 34.6741 9
244Pu → 244Am -73.1 ± 2.7 22 142.1535 47.1 42.5273 -52.6
243Am → 243Cm -6.9 ± 1.6 24 145.7401 114.8 43.621 12.7
246Bk → 246Cf -120 ± 60 23 153.124 10 45.845 -100

Second category: Qβ−>0 for neutral atoms

Here we only consider the nuclides with Qβ−(ZAX)<200keV. There are two cases:

∙ There are excited states of the daughter with energies lying between Qβ−(ZAX) and Qβ−(ZAXZ+), thus providing more channels to decay when the parent is fully ionized: 187Re, 194Os, 227Ac, 241Pu, 247Cm, 250Cm, 249Bk.

∙ There are no such excited states, so full ionizing only increases beta-decay energies of the original paths: 210Pb, 212At, 222Rn*, 228Ra.

Beta decay Qβ−(ZAX) E(Z+1)−E(Z) IZ+1(Z+1) Qβ−(ZAXZ+) ∑i=12(IZ+2−i(Z+1)−IZ+1−i(Z))+IZ−1(Z+1) Qβ−(ZAX(Z−2)+)
187Re → 187Os* (9.756 keV) -7.289 ± 0.002 15.2 85.61442 63.125 25.7921 3.303

See here, Table IV for details.

* It is not clear which category should 222Rn be put into.

Bound-state 2β− decays

Similarly, we have Q2β−(ZAXn+)=Q2β−(ZAX)+∑i=1nIi(Z)−∑i=1nIi(Z+2), hence

Qβ−(ZAX(Z−n)+)=Qβ−(ZAX)−(E(Z+2)−E(Z))+∑i=1n(IZ+3−i(Z+2)−IZ+1−i(Z))+IZ+2−n(Z+2)+IZ+1−n(Z+2).

In particular, for n=0, we have Qβ−(ZAXZ+)≈Qβ−(ZAX)−(E(Z+2)−E(Z))+2IZ+2(Z+2);

for n=1, we have Qβ−(ZAX(Z−1)+)≈Qβ−(ZAX)−(E(Z+2)−E(Z))+IZ+2(Z+2)+IZ(Z+2).

Double beta decay Q2β−(ZAX) E(Z+2)−E(Z) IZ+2(Z+2)+IZ+1(Z+2) Q2β−(ZAXZ+) (IZ+2(Z+2)−IZ(Z))+IZ+1(Z+2)+IZ(Z+2) Q2β−(ZAX(Z−1)+)
152Sm → 152Gd -55.7 22.96 116.84945 38.2 75.85972 -2.8
164Dy → 164Er -25.0 25.2 133.08972 82.9 86.29105 36.1
214Po → 214Rn -150 37.1 223.6886 37 144.6083 -42
242Pu → 242Cm -86.8 46 289.051 156.3 186.9038 54.1

Nuclides with the lowest mass among isobars of mass numbers 141 ~ 209

For 141 ≤ A ≤ 209, the nuclide with the lowest mass among isobars of A (141Pr, 142Nd, 143Nd, 144Nd, 145Nd, 146Sm, ..., 209Bi) are of particular interest. The following table lists their predicted half-lives here:

A Nuclide log Tα (yr)
146 146Sm 7.96
147 147Sm 11.03
186 186Os 15.30
144 144Nd 15.36
148 148Sm 15.80
187 187Os 17.66
149 149Sm 18.47
151 151Eu 18.66
209 209Bi 19.30
176 176Hf 20.51
177 177Hf 22.00
145 145Nd 22.93
192 192Pt 22.96
178 178Hf 23.64
185 185Re 25.02
188 188Os 26.28
150 150Sm 28.05
191 191Ir 29.09
170 170Yb 29.24
189 189Os 31.18
179 179Hf 31.31
182 182W 32.82
175 175Lu 35.28
184 184W 35.97
204 204Pb 36.01
171 171Yb 36.50
181 181Ta 38.78
183 183W 39.46
172 172Yb 42.34
194 194Pt 44.47
180 180Hf 45.84
190 190Os 47.39
169 169Tm 47.63
198 198Hg 52.15
154 154Gd 52.60
173 173Yb 62.37
195 195Pt 64.13
166 166Er 64.52
206 206Pb 66.55
193 193Ir 67.00
197 197Au 71.78
174 174Yb 75.31
203 203Tl 80.57
167 167Er 80.96
196 196Pt 82.67
199 199Hg 83.82
143 143Nd 88.12
168 168Er 91.90
200 200Hg 95.46
153 153Eu >100
160 160Dy >100
152 152Sm >100
155 155Gd >100
156 156Gd >100
208 208Pb >100
161 161Dy >100
157 157Gd >100
207 207Pb >100
159 159Tb >100
158 158Gd >100
165 165Ho >100
162 162Dy >100
201 201Hg >100
163 163Dy >100
142 142Nd >100
202 202Hg >100
164 164Er >100
205 205Tl >100
141 141Pr >100

For nuclides in the table with predicted alpha half-lives longer than 10100 years (including being stable to alpha decay), cluster decay modes (for example 16O emission) must be taken into account when modeling the half-lives. It seems that there is no concensus on predicting cluster decay half-lives, in contrast to alpha decay.

Warning: The following table is purely insane and contains nothing serious.

My guess of cluster decay half-lives
Nuclide log Tα (yr) log T12C (yr) log T14C (yr) log T18O (yr) log T24Ne (yr) minimum
141Pr - 245.75 - 210.85 291.50 210.85
205Tl 283.07 201.02 201.97 219.02 226.19 201.02
164Dy - 204.89 210.06 206.46 187.41 187.41
202Hg 305.64 188.90 186.02 204.49 215.28 186.02
142Nd - 188.35 498.81 185.32 253.31 185.32
163Dy - 193.71 202.49 190.41 181.18 181.18
201Hg 171.10 174.61 173.33 190.21 210.54 171.10
162Dy 336.47 171.38 175.29 171.00 173.99 171.00
165Ho 242.65 169.21 194.22 188.44 187.58 169.21
158Gd - 175.63 159.36 166.90 178.65 159.36
159Tb - 159.93 157.32 157.48 179.61 157.32
207Pb 157.17 193.02 198.06 215.52 230.38 157.17
157Gd - 150.39 144.38 152.04 181.80 144.38
161Dy 132.24 156.10 160.63 157.78 175.85 132.24
208Pb 128.87 203.20 202.37 223.74 236.49 128.87
156Gd - 127.89 130.31 139.36 182.19 127.89
155Gd 304.37 111.31 117.55 127.23 184.32 111.31
152Sm 164.24 115.84 111.23 127.65 187.96 111.23
160Dy 110.29 135.61 144.68 145.50 177.93 110.29
153Eu 144.69 108.55 110.99 122.63 186.92 108.55

I wish 4He had energy 6 MeV higher

Then α decays would essentially disappear. Warning: The following table is purely insane and contains nothing serious.

My guess of decay modes without α decay
Nuclide Q8Be (MeV) log T8Be (yr) Q12C (MeV) log T12C (yr) Q14C (MeV) log T14C (yr) minimum
215At 14.84 12.03 21.89 26.09 22.13 25.62 12.03
212Rn 11.51 19.88 20.84 28.16 19.28 31.22 19.88
214Rn 14.52 12.78 23.03 23.85 22.16 25.56 12.78
216Rn 17.06 6.79 24.94 20.10 24.58 20.81 6.79
217Rn 16.33 8.51 25.95 18.11 25.91 18.19 8.51
218Rn 15.00 11.65 26.16 17.70 26.89 16.27 11.65
220Rn 13.22 15.85 23.71 22.52 28.54 13.02 13.02
222Rn 11.61 19.64 21.49 26.88 26.45 17.13 17.13
219Fr 15.53 10.40 29.65 10.84 29.42 11.29 10.40
218Ra 17.66 5.38 30.43 9.31 28.74 12.63 5.38
220Ra 15.70 10.00 32.02 6.18 31.04 8.11 6.18
221Ra 14.68 12.40 30.58 9.01 32.40 5.44 5.44
222Ra 13.85 14.36 29.05 12.02 33.05 4.16 4.16
223Ra 12.83 16.77 27.72 14.63 31.83 6.56 6.56
224Ra 12.10 18.49 26.37 17.29 30.53 9.11 9.11
226Ra 10.37 22.57 23.85 22.24 28.20 13.69 13.69
225Ac 12.30 18.02 26.87 16.30 30.48 9.21 9.21
224Th 14.80 12.12 30.36 9.45 32.93 4.39 4.39
226Th 13.04 16.27 27.67 14.73 30.55 9.07 9.07
228Th 11.22 20.56 24.99 20.00 28.20 13.65 13.65

The primary decay mode of 226Th without α decay would perhaps be 18O emission (unknown in the real world).

The primary decay mode of 228Th without α decay would be 20O emission (known in the real world; the partial half-life is 1.69×1013 years).

The primary decay mode of 230U without α decay would be 22Ne emission (known in the real world; the partial half-life is 1.15×1012 years).

The primary decay mode of 232U without α decay would be 24Ne emission (known in the real world; the partial half-life is 7.74×1012 years).

Hands in Poker

Imagine that an online system of Poker allows players to customize the number of suits d and the number of ranks n. What should be the ranking of hands in the game?

By the way, a straight means five cards with consecutive ranks. However, the highest-ranking card can be used as high or low in a straight, and thus there are n−3 of them in terms of card values.

∙ For the standard deck, the card ranking is 2 3 4 5 6 7 8 9 10 J Q K A, hence the lowest-ranking straight is A2345;

∙ In Six-plus hold 'em, the card ranking is 6 7 8 9 10 J Q K A, hence the lowest-ranking straight is A6789;

∙ In the deck of Five Crowns, the card ranking is 3 4 5 6 7 8 9 10 J Q K, hence the lowest-ranking straight is K3456.

When we pick randomly 5 cards from a deck with general n and d, the number of combinations of each hand is given as follows. A hand having a smaller number of combinations in the table ranks higher, except that a pair always beats high card (even if high card occurs less often if

{n≤11,d=4;n≤12,d=5,6,7,8,9;n≤13,d≥10.

The concrete mode of game (Texas, Omaha, or anything original) is irrelevant to the determination of ranking of hands.

Hand Card value type Suit combinations of hand Card value combinations of hand
Straight flush 1+1+1+1+1 d n−3
Five of a kind 5 (d5) n
Four of a kind 4+1 (d4)d n(n−1)
Full house 3+2 (d3)(d2) n(n−1)
Flush 1+1+1+1+1 d (n5)−(n−3)
Straight 1+1+1+1+1 d5−d n−3
Three of a kind 3+1+1 (d3)d2 n(n−1)(n−2)2
Two pairs 2+2+1 (d2)2d n(n−1)(n−2)2
One pair 2+1+1+1 (d2)d3 n(n−1)(n−2)(n−3)6
High card 1+1+1+1+1 d5−d (n5)−(n−3)
Total (= ∑ suit combinations × card value combinations) (dn5)

Please note that we cannot add a hand that "contains one card in each suit" for d≥5 because, as d→∞, 100% of draws of 5 cards consist of 5 cards in different suits. This is a special case of a principle when setting the list of hands: a hand is only valuable when it contains "similarities", not "differences".

Other observations should be mentioned. We always have

∙ Straight flush > Four of a kind > Full house > Straight > Three of a kind > Two pairs > One pair > High card for d≤4;

∙ Five of a kind > Straight flush > Four of a kind > Full house > Straight > Three of a kind > Two pairs > One pair > High card for d=5; and

∙ Straight flush > Five of a kind > Four of a kind > Full house > Straight > Three of a kind > Two pairs > One pair > High card for d≥5,

but the positions of a flush and a straight depend on the specific value of n. A flush can rank anywhere between a straight flush and high card, while a straight can only rank below a five-of-a-kind and above a three-of-a-kind. The turning point of the positions of

∙ a flush and a full house is n=1013d43−34×1013d13+3+o(1) as d→∞;

∙ a flush and a straight is n=12014d+74+o(1) as d→∞;

∙ evidently enough, a five-of-a-kind ranks lower than a flush if n≤d and higher if n>d (hence the turning point is n=d∼d+1).

Turning points for specific d:

∙d=4: a flush and a full house change positions at n=12∼13, and a flush and a straight change positions at n=15∼16;

∙d=5: a flush and a four-of-a-kind change positions at n=11∼12, and a flush and a full house change positions at n=16∼17;

∙d=6: a flush and a four-of-a-kind change positions at n=13∼14.

Notice. Somebody may think that the ranking of hands should be determined by 7-card combinations rather than 5-card combinations, since Poker is a game of seeing 7 cards. The problem is, a 7-card combination contains in general 5-card combinations in different categories, so how to assess the value of each 7-card combination? In other words, the number of 7-card combinations of each hand can only be calculated after the determination of the ranking, not before. Since combinations of higher rankings need to be deducted while determining the number of each 7-card combination, those numbers no longer reflect the probability of getting each hand.

Standard deck (n=13, d=4)

Hand Combinations
Straight flush 40
Four of a kind 624
Full house 3744
Flush 5108
Straight 10200
Three of a kind 54912
Two pairs 123552
One pair 1098240
High card 1302540
Total 2598960

Six-plus hold 'em (n=9, d=4)

In the game Six-plus hold 'em, there are only 9 card values used: 6 7 8 9 10 J Q K A from the lowest to the highest.

Hand Combinations
Straight flush 24
Four of a kind 288
Flush 480
Full house 1728
Straight 6120
Three of a kind 16128
Two pairs 36288
One pair 193536
High card 122400
Total 376992

Deck of French Tarot (n=14, d=4)

The only commercially available deck of playing cards with more than 13 cards in each suit. It is difficult for people from other countries to imagine just how much the French enjoy playing tarot.

Hand Combinations
Straight flush 44
Four of a kind 728
Full house 4368
Flush 7964
Straight 11220
Three of a kind 69888
Two pairs 157248
One pair 1537536
High card 2030820
Total 3819816

Deck of Uno No Mercy (n=16, d=4)

In a deck of Uno No Mercy each color contains 16 kinds of different cards: 0-9, Reverse, Skip, Draw 2, Draw 4, Skip Everyone, Discard All. I list this pair of (n,d) here because n=16 is the least value such that a straight beats a flush.

Hand Combinations
Straight flush 52
Four of a kind 960
Full house 5760
Straight 13260
Flush 17420
Three of a kind 107520
Two pairs 241920
One pair 2795520
High card 4442100
Total 7624512

Deck of Five Crowns (n=11, d=5)

The only commercially available deck of playing cards with more than 4 suits. A quite niche board game.

Hand Combinations
Five of a kind 11
Straight flush 40
Flush 2270
Four of a kind 2750
Full house 11000
Straight 24960
Three of a kind 123750
Two pairs 247500
One pair 1650000
High card 1416480
Total 3478761

Non-uniqueness of the par contract in contract bridge

Have you noticed that in rare cases, when some suit is fixed to be the trump suit, the number of tricks for N/S (the number of tricks which can be taken by NS if either N or S is the declarer) and the number of tricks for E/W can add up to more than 13? If so, the par contract may depend on who bids first! (See here for examples!)

First let's think about the question of finding the par contract in general. Here, instead of comparing contracts that either side can make, we compare the double dummy result. I will write, say, "we have the condition C=9", to mean if club is the trump suit, then the double dummy result is that when either I and my partner is the declarer, the optimal result for us is exactly 9 tricks.

Let A be the highest-ranking condition (in the sequence C=7, D=7, H=7, S=7, NT=7, ..., C=13, D=13, H=13, S=13, NT=13) that we have, and B be the highest-ranking condition that the opponents have. Suppose WLOG that A ranks higher than or equal to B. Now we list all the conditions we have that rank at least as high as B, then left over the most valuable ones. The least to the most valuable conditions are as follows:

C=7, D=7
H=7, S=7
NT=7, C=8, D=8
H=8, S=8, C=9, D=9
NT=8
C=10, D=10
H=9, S=9
NT=9, C=11, D=11
H=10, S=10
NT=10
H=11, S=11
NT=11
C=12, D=12
H=12, S=12
NT=12
C=13, D=13
H=13, S=13
NT=13

The resulting conditions reflect the ideal contract in the bidding process if sacrifice bids are not used. I call these conditions the optimal conditions of a deal.

Now we check the double dummy result of our opponents in the suits of the optimal conditions. Pick the highest-ranking (in the sequence C=0, D=0, H=0, S=0, NT=0, ..., C=13, D=13, H=13, S=13, NT=13) condition (call it B'). If B'+1 ranks higher than B (if B' is, say, C=7, then B'+1 is the condition C=8), then the suit of B' is the key suit. If the number of tricks for N/S and the number of tricks for E/W add up to more than 13 given that the key suit is the trump suit, then it is very likely that the par contract depends on which side bids first!

See these very long tables made by me for more details.

Table of minimal polynomial of -2 cos(2π/n) (note the minus sign!)

Let Pn be the minimal polynomial of −2cos⁡2πn for n ≥ 3, and P1 = P2 := 1. Then we have:

∏d|nPd=(X−110)2,1n/2 for even n; ∏d|nPd=(X−110)1,1(n−1)/2+(X−110)1,2(n−1)/2 for odd n.

PARI code:

Prod(n) = my(M = [X,-1;1,0]); if(n%2==0, (M^(n/2))[2,1], (M^((n-1)/2) * [1;1])[1,1])
P(n) = my(P = 1); fordiv(n, d, P *= Prod(n/d)^moebius(d)); P
n Pn Pn(k) for k = 3 k = 4 k = 6
3 X−1 2 3 5
4 X 3 4 6
5 X2−X−1 5 11 29
6 X+1 4 5 7
7 X3−X2−2X+1 13 41 169
8 X2−2 7 14 34
9 X3−3X−1 17 51 197
10 X2+X−1 11 19 41
11 X5−X4−4X3+3X2+3X−1 89 571 5741
12 X2−3 6 13 33
13 X6−X5−5X4+4X3+6X2−3X−1 233 2131 33461
14 X3+X2−2X−1 29 71 239
15 X4+X3−4X2−4X+1 61 241 1345
16 X4−4X2+2 47 194 1154
17 X8−X7−7X6+6X5+15X4−10X3−10X2+4X+1 1597 29681 1136689
18 X3−3X+1 19 53 199
19 X9−X8−8X7+7X6+21X5−15X4−20X3+10X2+5X−1 4181 110771 6625109
20 X4−5X2+5 41 181 1121

Let p be an odd prime not dividing k2 - 4, then there exists a unique number of the form α(k,p)=p−(k2−4p)m≥3 such that p divides Pα(k,p)(k). The parity of m is determined by the value of (−(k−2)p). Consider the case k = 4, so k2 - 4 = 12 and -(k - 2) = -2:

p 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
corresponding m 1 1 2 1 2 2 1 1 1 1 6 2 1 3 2 1 4 5 2 1 2 2 6
(−(k−2)p) -1 -1 1 -1 1 1 -1 -1 -1 -1 1 1 -1 -1 1 -1 1 -1 1 -1 1 1 1

(Also, you may find this document written by myself interesting. At the end of page 4, there is a conjecture on the densities of the occurrences of α(k,p) odd, α(k,p) ≡ 2 (mod 4), and 4 | α(k,p)).

Wall-Sun-Sun primes in Lucas sequences

Let T(P,Q,n) be the n-th term of the Lucas sequence (P,Q) of the first kind, then we have T(k,1,n)=T(k−2,−1,2n)k−2 for k ≥ 3. For odd primes p that are not factors of k2 - 4 (so that p−(k2−4p) is even), we always have p∣T(k−2,−1,p−(k2−4p))k−2=T(k,1,p−(k2−4p)2), so it would be meaningful to ask when p2 divides this quantity. The n-Wall-Sun-Sun primes correspond to k = n2 + 2.

Note the product formula T(k−2,−1,n)k−2=∏d|n,d≥3Pd(k) for even n and T(k−2,−1,n)=∏d|n,d≥3Pd(k) for odd n, where Pn is the minimal polynomial of −2cos⁡2πn.

The OEIS has A238490 for k = 4, A238736 for k = 6 and A337791 for k = 38.

Numbering of flags in Endless mode of Plants vs. Zombies

Let x (a 32-bit signed integer) be the number of the current level. Set y=20⋆x (32-bit signed multiplication), then:

∙ The level x starts at flag y/10 (32-bit signed integer division) and ends at flag y/10+2. This will be written as flags [y/10,y/10+2) in the table at the end.

∙ For w=1,⋯,20, the w-th flag of level x has zombies if and only if y+w=−1,0,⋯,1073741824 (32-bit signed addition) or y+w=2147483647,−2147483648,⋯,−1073741824. Only Flag Zombies appear for waves not in these ranges.

∙ For Pool and Fog settings, the game crashes on a level when there are no zombies other than Flag Zombies in the 20 waves.

Let's look at x=53687091 for an example. We have y=1073741820, so we start at flag 107374182 and end at flag 107374184. Notice: The next level crashes with Pool or Fog because there would be no zombies. That's why many believe that the game only has 107374184 flags, which is of course not true (just try Day, Night, or Roof).

Wave w 1 2 3 4 5 ... 20
y+w 1073741821 1073741822 1073741823 1073741824 1073741825 ... 1073741840
Has zombies? Yes Yes Yes Yes No ... No

Look at also x=107374182. Then y=2147483640, so we start at flag 214748364 and end at flag 214748366. Warning: The next level starts at flag −214748363 as we plug in x=107374183.

Wave w 1 2 3 4 5 6 7 8 ... 20
y+w 2147483641 2147483642 2147483643 2147483644 2147483645 2147483646 2147483647 -2147483648 ... -2147483636
Has zombies? No No No No No No Yes Yes ... Yes

A summarizing table:

These waves are normal (-1~1073741824)

These waves have only Flag Zombies (game crash with Pool or Fog) (1073741825~2147483646, -1073741823~-2)

These waves are somehow normal (2147483647~-1073741824)

Period Quarter-period Levels # of levels Flags contained Wave numbers
1 1a 0~53687091 53687092 [0,107374184) Levels 0~53687090 (flags [0,107374182)): 1~1073741820
Level 53687091 (flags [107374182,107374184)): 1073741821~1073741824, 1073741825~1073741840
1b 53687092~107374182 53687091 [107374184,214748366) Levels 53687092~107374181 (flags [107374184,214748364)): 1073741841~2147483640
Level 107374182 (flags [214748364,214748366)): 2147483641~2147483646, 2147483647~-2147463636
1c 107374183~161061273 53687091 [-214748363,-107374181) Levels 107374183~161061272 (flags [-214748363,-107374183)): -2147483635~-1073741836
Level 161061273 (flags [-107374183,-107374181)): -1073741835~-1073741824, -1073741823~-1073741816
1d 161061274~214748364 53687091 [-107374181,1) Levels 161061274~214748363 (flags [-107374181,-1)): -1073741815~-16
Level 214748364 (flags [-1,1)): -15~-2, -1~4
2 2a 214748365~268435455 53687091 [0,107374182) Levels 214748365~268435455 (flags [0,107374182)): 5~1073741824
2b 268435456~322122547 53687092 [107374182,214748366) Levels 268435456~322122546 (flags [107374182,214748364)): 1073741825~2147483644
Level 322122547 (flags [214748364,214748366)): 2147483645~2147483646, 2147483647~-2147483632
2c 322122548~375809638 53687091 [-214748363,-107374181) Levels 322122548~375809637 (flags [-214748363,-107374183)): -2147483631~-1073741832
Level 375809638 (flags [-107374183,-107374181)): -1073741831~-1073741824, -1073741823~-1073741812
2d 375809639~429496729 53687091 [-107374181,1) Levels 375809639~429496728 (flags [-107374181,-1)): -1073741811~-12
Level 429496729 (flags [-1,1)): -11~-2, -1~8
3 3a 429496730~483183820 53687091 [0,107374182) Levels 429496730~483183819 (flags [0,107374180)): 9~1073741808
Level 483183820 (flags [107374180,107374182)): 1073741809~1073741824, 1073741825~1073741828
3b 483183821~536870911 53687091 [107374182,214748364) Levels 483183821~536870910 (flags [107374182,214748362)): 1073741829~2147383628
Level 536870911 (flags [214748362,214748364)): 2147483629~2147483646, 2147483647~-2147483648
3c 536870912~590558003 53687092 [-214748364,-107374180) Levels 536870912~590558002 (flags [-214748364,-107374182)): -2147483647~-1073741828
Level 590558003 (flags [-107374182,-107374180)): -1073741827~-1073741824, -1073741823~-1073741808
3d 590558004~644245094 53687091 [-107374180,2) Levels 590558004~644245093 (flags [-107374180,0)): -1073741807~-8
Level 644245094 (flags [0,2)): -7~-2, -1~12
4 4a 644245095~697932185 53687091 [1,107374183) Levels 644245095~697932184 (flags [1,107374181)): 13~1073741812
Level 697932185 (flags [107374181,107374183)): 1073741813~1073741824, 1073741825~1073741832
4b 697932186~751619276 53687091 [107374183,214748365) Levels 697932186~751619275 (flags [107374183,214748363)): 1073741833~2147483632
Level 751619276 (flags [214748363,214748365)): 2147483633~2147483646, 2147483647~-2147483644
4c 751619277~805306367 53687091 [-214748364,-107374182) Levels 751619277~805306367 (flags [-214748364,-107374182)): -2147483643~-1073741824
4d 805306368~858993459 53687092 [-107374182,2) Levels 805306368~858993458 (flags [-107374182,0)): -1073741823~-4
Level 858993459 (flags [0,2)): -3~-2, -1~16
5 5a 858993460~912680550 53687091 [1,107374183) Levels 858993460~912680549 (flags [1,107374181)): 17~1073741816
Level 912680550 (flags [107374181,107374183)): 1073741816~1073741824, 1073741825~1073741836
5b 912680551~966367641 53687091 [107374183,214748365) Levels 912680551~966367640 (flags [107374183,214748363)): 1073741837~2147483636
Level 966367641 (flags [214748363,214748365)): 2147483637~2147483646, 2147483647~-2147483640
5c 966367642~1020054732 53687091 [-214748364,-107374182) Levels 966367642~1020054731 (flags [-214748364,-107374184)): -2147483639~-1073741840
Level 1020054732 (flags [-107374184,-107374182)): -1073741839~-1073741824, -1073741823~-1073741820
5d 1020054733~1073741823 53687091 [-107374182,0) Levels 1020054733~1073741822 (flags [-107374182,-2)): -1073741819~-20
Level 1073741823 (flags [-2,0)): -19~-2, -1~0

List of telephone number ranges

I: 134Ba 135Ba 136Ba 137Ba 138Ba 139La 147Sm 150Sm 151Eu 152Sm 157Gd 158Gd 159Tb 172Yb 178Hf 182W 183W 184W 187Os 188Os 195Pt 197Au 198Hg

II: 130Xe 131Xe 132Xe 155Gd 156Gd 166Er 175Lu 176Hf 185Re 186Os 196Pt

III: 133Cs 153Eu 173Yb 177Hf 180Hf 181Ta 189Os 190Os 191Ir 193Ir 199Hg

IV: 192Pt

Virtual: 162Dy 165Ho 167Er 170Yb 171Yb

Factoring rational primes on the quadratic number field with discriminant D