This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A023256 #31 Mar 27 2025 05:20:25 %S A023256 2,17,47,61,101,131,151,331,367,461,607,751,937,971,1151,1321,1327, %T A023256 1361,1481,1511,1607,1811,1847,1907,2081,2287,2347,2357,2791,2851, %U A023256 2971,3251,3257,3457,3491,3581,3761,4007,4091,4127,4861,4967,5231,5347,5387,5407 %N A023256 Primes that remain prime through 2 iterations of function f(x) = 6x + 1. %C A023256 Primes p such that 6*p+1 and 36*p+7 are also primes. - _Vincenzo Librandi_, Aug 04 2010 %C A023256 Subsequence of A007693. - _Michel Marcus_, Oct 17 2015 %H A023256 John Cerkan, <a href="/A023256/b023256.txt">Table of n, a(n) for n = 1..10000</a> %F A023256 a(n) == 1 or 7 (mod 10) for n > 1. - _John Cerkan_, Sep 14 2016 %t A023256 Select[Prime[Range[800]],AllTrue[Rest[NestList[6#+1&,#,2]],PrimeQ]&] (* _Harvey P. Dale_, Oct 17 2020 *) %o A023256 (Magma) [n: n in [0..100000] | IsPrime(n) and IsPrime(6*n+1) and IsPrime(36*n+7)] // _Vincenzo Librandi_, Aug 04 2010 %o A023256 (PARI) lista(nn) = forprime(n=1, nn, if (isprime(p=6*n+1) && isprime(6*p+1), print1(n, ", "))); \\ _Michel Marcus_, Oct 17 2015 %Y A023256 Cf. A007693 (1 iteration), A023287 (3 iterations). %K A023256 nonn %O A023256 1,1 %A A023256 _David W. Wilson_