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A255229
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Integers n such that n^2 - 1 is the difference of the squares of twin primes.
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0
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5, 7, 11, 13, 17, 31, 41, 43, 49, 77, 83, 101, 109, 119, 133, 179, 203, 263, 277, 283, 307, 311, 329, 353, 377, 407, 413, 419, 431, 437, 463, 473, 493, 577, 581, 619, 629, 703, 757, 791, 811, 907, 911, 913, 991, 1001, 1037, 1061, 1103, 1121, 1249, 1289, 1337, 1373, 1441, 1457, 1487, 1523, 1597, 1651, 1781
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OFFSET
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1,1
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LINKS
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EXAMPLE
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31^2 - 1 = 241^2 - 239^2, and (239, 241) is a twin prime pair, so 31 is in the sequence.
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MATHEMATICA
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lst={}; f[n_]:=Sqrt[Prime[n]^2-NextPrime[Prime[n], -1]^2+1];
Do[If[Prime[n]-NextPrime[Prime[n], -1]==2&&IntegerQ[f[n]], AppendTo[lst, f[n]]], {n, 3, 10^5}]; lst (* Ivan N. Ianakiev, Mar 30 2015 *)
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PROG
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(PARI) lista(nn) = {forprime(p=3, nn, q = precprime(p-1); if (((p-q) == 2) && issquare(d=p^2-q^2+1), print1(sqrtint(d), ", ")); ); } \\ Michel Marcus, Feb 18 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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