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 A347886 #11 Sep 19 2021 22:02:26 %S A347886 1,7,9,11,13,15,19,23,25,29,31,43,47,51,53,63,67,73,77,79,81,83,85,91, %T A347886 97,99,103,105,111,113,117,121,123,127,133,135,143,147,157,161,163, %U A347886 165,171,175,177,179,183,185,191,195,197,199,203,205,207,209,211,213,217,223,225,227,233,239,241,243,245,247,251,253 %N A347886 Odd numbers k such that sigma(k^2) has an even number of prime factors when counted with multiplicity. %C A347886 Equally, odd numbers k such that A003415(sigma(k^2)) is even, i.e., k^2 is in A347878. See A235991. %H A347886 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a> %t A347886 Select[Range[1, 250, 2], EvenQ[PrimeOmega[DivisorSigma[1, #^2]]] &] (* _Amiram Eldar_, Sep 19 2021 *) %o A347886 (PARI) isA347886(n) = ((n%2)&&!(bigomega(sigma(n^2))%2)); %Y A347886 Cf. A000203, A001222, A003415, A005820, A235991, A342923, A342925, A347391, A347870, A347878, A347882, A347885 (complement among A005408). %K A347886 nonn %O A347886 1,2 %A A347886 _Antti Karttunen_, Sep 19 2021