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 A324899 #17 Apr 05 2024 08:17:12 %S A324899 25,169,225,289,841,1225,1369,1521,1681,2025,2601,2809,3025,3721,5329, %T A324899 7569,7921,8281,9025,9409,10201,11025,11881,12321,12769,13225,13689, %U A324899 14161,15129,15625,18225,18769,20449,22201,23409,24025,24649,25281,27225,29929,32761,33489,34969,37249,38809,41209,46225,47961,52441,54289,55225 %N A324899 Odd numbers k for which sigma(k) == 3 (mod 4). %C A324899 These are all squares. Square roots are in A324909. %H A324899 Antti Karttunen, <a href="/A324899/b324899.txt">Table of n, a(n) for n = 1..10000</a> %H A324899 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>. %F A324899 a(n) = A324909(n)^2. - _Amiram Eldar_, Apr 05 2024 %t A324899 Select[Range[1, 235, 2]^2, Mod[DivisorSigma[1, #], 4] == 3 &] (* _Amiram Eldar_, Apr 05 2024 *) %o A324899 (PARI) isA324899(n) = ((n%2)&&3==(sigma(n)%4)); %Y A324899 Intersection of A016754 and A072462. %Y A324899 Cf. A000203, A324909 (square roots). %Y A324899 Cf. A325311 (a subsequence). %K A324899 nonn %O A324899 1,1 %A A324899 _Antti Karttunen_, Apr 20 2019