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 A007638 M5129 #23 Sep 08 2022 08:44:35 %S A007638 23,24,28,31,39,44,45,46,47,50,52,56,57,60,63,67,69,70,71,79,80,85,86, %T A007638 88,89,90,92,93,96,97,102,107,108,112,115,116,118,119,121,122,123,126, %U A007638 128,131,134,137,138,139,143,144,145,147,148,151,153,156,157,161,162 %N A007638 Numbers k such that 3*k^2 - 3*k + 23 is composite. %D A007638 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A007638 Vincenzo Librandi, <a href="/A007638/b007638.txt">Table of n, a(n) for n = 1..3100</a> %H A007638 H. Dubner, <a href="/A005849/a005849.pdf">Generalized Cullen numbers</a>, J. Rec. Math., 21 (No. 3, 1989), 190-191. (Annotated scanned copy) %t A007638 Select[Range[200], !PrimeQ[3 #^2 - 3 # + 23] &] (* _Vincenzo Librandi_, Jun 08 2017 *) %o A007638 (PARI) is(n)=!isprime(3*n^2 - 3*n + 23) \\ _Charles R Greathouse IV_, Oct 23 2015 %o A007638 (Magma) [n: n in [0..200]| not IsPrime(3*n^2-3*n+23)]; // _Vincenzo Librandi_, Jun 08 2017 %K A007638 nonn,easy %O A007638 1,1 %A A007638 _N. J. A. Sloane_, _Mira Bernstein_, _Robert G. Wilson v_