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 A023251 #32 Mar 14 2025 15:30:07 %S A023251 7,41,43,47,67,71,97,103,137,263,293,307,397,421,467,491,571,587,593, %T A023251 683,727,757,883,907,1021,1061,1063,1097,1153,1373,1427,1433,1453, %U A023251 1523,1567,1657,1747,1811,1867,2141,2251,2281,2287,2647,2693,2791,2797,2857,2927 %N A023251 Primes that remain prime through 2 iterations of function f(x) = 4x + 9. %C A023251 Primes p such that 4*p+9 and 16*p+45 are also primes. - _Vincenzo Librandi_, Aug 04 2010 %H A023251 John Cerkan, <a href="/A023251/b023251.txt">Table of n, a(n) for n = 1..10000</a> %t A023251 rpQ[n_]:=AllTrue[Rest[NestList[4#+9&,n,2]],PrimeQ]; Select[Prime[ Range[ 500]],rpQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, May 03 2019 *) %o A023251 (Magma) [n: n in [0..100000] | IsPrime(n) and IsPrime(4*n+9) and IsPrime(16*n+45)]; // _Vincenzo Librandi_, Aug 04 2010 %Y A023251 Subsequence of A111199. %K A023251 nonn %O A023251 1,1 %A A023251 _David W. Wilson_