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 A241266 #14 Sep 08 2022 08:46:07 %S A241266 6,7,9,11,16,17,18,20,21,26,29,31,36,37,39,40,41,42,44,45,46,49,51,52, %T A241266 53,54,55,56,58,59,61,62,64,66,68,71,73,75,76,78,81,83,84,85,86,89,91, %U A241266 95,96,97,99,100,101,102,104,105,106,107,108,111,112,113,114 %N A241266 Numbers n such that 4*n^2+2*n-1 is not prime. %H A241266 Vincenzo Librandi, <a href="/A241266/b241266.txt">Table of n, a(n) for n = 1..1000</a> %e A241266 7 is in this sequence because 4*7^2+2*7-1 = 209 = 11*19. %t A241266 Select[Range[200], ! PrimeQ[4 #^2 + 2 # - 1] &] %o A241266 (Magma) [n: n in [1..150] |not IsPrime(4*n^2+2*n-1)]; %Y A241266 Complement of A155736. %K A241266 nonn,easy %O A241266 1,1 %A A241266 _Vincenzo Librandi_, Apr 20 2014