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 A356449 #16 Aug 08 2022 09:15:33 %S A356449 1,2,4,5,7,8,11,13,14,16,17,19,20,22,23,25,26,29,31,32,34,35,37,38,41, %T A356449 43,44,46,47,49,52,53,55,56,58,59,61,62,64,65,67,68,71,73,74,76,79,80, %U A356449 82,83,85,86,88,89,91,92,94,95,97,98,100,101,103,104,106,107,109,112,113 %N A356449 Numbers k such that 2*k^2 is in A014567. %C A356449 Numbers k such that k and sigma(2*k^2) are coprime, sigma = A000203. %C A356449 No term can be a multiple of 3 since 3 divides sigma(m) if m is twice a square (cf. A065766). %H A356449 Jianing Song, <a href="/A356449/b356449.txt">Table of n, a(n) for n = 1..11086</a> (all terms <= 20000) %e A356449 20 is a term since 20 and sigma(2*20^2) = 1953 are coprime. %o A356449 (PARI) isA356449(n) = gcd(n,sigma(2*n^2))==1 %Y A356449 Cf. A014567, A000203, A356382, A356448, A356451, A356453 (complement), A065766. %K A356449 nonn,easy %O A356449 1,2 %A A356449 _Jianing Song_, Aug 07 2022