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 A176256 #22 Apr 24 2021 08:44:35 %S A176256 9,21,33,45,49,57,69,77,81,93,105,117,121,129,133,141,153,161,165,177, %T A176256 189,201,209,213,217,225,237,249,253,261,273,285,297,301,309,321,329, %U A176256 333,341,345,357,361,369,381,393,405,413,417,429,437,441,453,465,469 %N A176256 Numbers of the form 4k+1 with least prime divisor of the form 4m-1. %C A176256 By definition, all terms are composite numbers. %C A176256 Cannot be the hypotenuse of a primitive Pythagorean triangle. - _Robert G. Wilson v_, Mar 16 2014 %H A176256 Vincenzo Librandi, <a href="/A176256/b176256.txt">Table of n, a(n) for n = 1..1000</a> %t A176256 fQ[n_] := Mod[ n, 4] == 1 && Mod[ FactorInteger[n][[1, 1]], 4] == 3; Select[Range@470, fQ] (* _Robert G. Wilson v_, Apr 08 2014 *) %o A176256 (PARI) isok(n) = ((n % 4) == 1) && (f = factor(n)) && ((f[1, 1] % 4) == 3); \\ _Michel Marcus_, Mar 16 2014 %Y A176256 Cf. A176255, A002148, A002145, A016813, A004767. %Y A176256 Complement of A020882 in 1 == Mod 4. %K A176256 nonn %O A176256 1,1 %A A176256 _Vladimir Shevelev_, Apr 13 2010 %E A176256 More terms from _Michel Marcus_, Mar 16 2014