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 A176257 #12 Nov 27 2019 05:32:06 %S A176257 15,39,51,75,87,91,111,119,123,135,143,159,183,187,195,203,219,255, %T A176257 259,267,287,291,303,319,327,339,351,371,375,407,411,427,435,447,451, %U A176257 455,459,471,507,511,519,543,551,555,579,583,591,595,615,623,663,667,671 %N A176257 Numbers of the form 4k-1 with greatest prime divisor of the form 4m+1. %C A176257 By definition, all terms are composite numbers. %H A176257 Amiram Eldar, <a href="/A176257/b176257.txt">Table of n, a(n) for n = 1..10000</a> %t A176257 Select[4*Range[200]-1,Divisible[FactorInteger[#][[-1,1]]-1,4]&] (* _Harvey P. Dale_, May 17 2013 *) %o A176257 (PARI) isok(n) = ((n % 4) == 3) && ((vecmax(factor(n)[,1]) % 4) == 1); \\ _Michel Marcus_, Feb 07 2016 %Y A176257 Cf. A176256, A176255, A002148, A002145, A016813, A004767. %K A176257 nonn %O A176257 1,1 %A A176257 _Vladimir Shevelev_, Apr 13 2010 %E A176257 Corrected and extended by _Harvey P. Dale_, May 17 2013