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 A324909 #19 Apr 05 2024 08:17:01 %S A324909 5,13,15,17,29,35,37,39,41,45,51,53,55,61,73,87,89,91,95,97,101,105, %T A324909 109,111,113,115,117,119,123,125,135,137,143,149,153,155,157,159,165, %U A324909 173,181,183,187,193,197,203,215,219,229,233,235,241,245,247,257,259,261,267,269,273,277,281,285,287,291,293,295,299,303,313 %N A324909 Odd numbers k for which sigma(k^2) == 3 (mod 4). %C A324909 Odd numbers with an odd number of prime factors congruent to 1 modulo 4, or odd members of A209922. - _Charlie Neder_, Apr 24 2019 %H A324909 Antti Karttunen, <a href="/A324909/b324909.txt">Table of n, a(n) for n = 1..10000</a> %H A324909 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>. %F A324909 a(n) = sqrt(A324899(n)). %t A324909 Select[Range[1, 315, 2], Mod[DivisorSigma[1, #^2], 4] == 3 &] (* _Amiram Eldar_, Apr 05 2024 *) %o A324909 (PARI) isA324909(n) = ((n%2)&&3==(sigma(n*n)%4)); %Y A324909 Cf. A000203, A000196, A324899. %Y A324909 Cf. A325312 (a subsequence). %Y A324909 Cf. A209922 (a supersequence). %K A324909 nonn %O A324909 1,1 %A A324909 _Antti Karttunen_, Apr 20 2019