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 A356454 #9 Aug 08 2022 09:15:39 %S A356454 7,21,35,39,42,49,56,57,62,63,77,78,84,91,93,99,105,111,114,117,119, %T A356454 126,129,133,147,154,155,156,161,168,171,175,183,186,189,195,198,201, %U A356454 203,209,210,217,219,222,228,231,234,237,245,252,258,259,266,273,275,279,280,285 %N A356454 Numbers k such that 4*k^2 is not in A014567; complement of A356451. %C A356454 Numbers k such that k and sigma(4*k^2) are not coprime, sigma = A000203. %H A356454 Jianing Song, <a href="/A356454/b356454.txt">Table of n, a(n) for n = 1..12241</a> (all terms <= 40000) %F A356454 a(n) = A356452(n)/2. %e A356454 7 is a term since 7 and sigma(4*7^2) = 399 have a common factor 7. %o A356454 (PARI) isA356454(n) = gcd(n, sigma(4*n^2))>1 %Y A356454 Cf. A014567, A000203, A356448, A356452, A356453. %K A356454 nonn,easy %O A356454 1,1 %A A356454 _Jianing Song_, Aug 07 2022