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 A347873 #9 Sep 18 2021 22:04:43 %S A347873 1,2,3,4,7,10,11,15,16,19,20,21,23,26,27,31,32,33,34,35,39,40,43,47, %T A347873 49,51,52,55,57,58,59,63,64,65,67,68,69,71,72,74,75,77,79,80,81,82,83, %U A347873 85,87,90,91,93,95,98,99,103,104,105,106,107,111,115,116,119,121,122,123,125,127,128,129,131,133,135,136 %N A347873 Numbers k such that k and A003415(sigma(k)) are of different parity. %C A347873 Numbers k for which A347870(k) differs from A000035(k). %t A347873 ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[136], Mod[ad[DivisorSigma[1, #]], 2] != Mod[#, 2] &] (* _Amiram Eldar_, Sep 18 2021 *) %Y A347873 Cf. A000035, A000203, A003415, A342925, A347870. %Y A347873 Positions of ones in A347871 (the characteristic function). A347872 gives the complement. %K A347873 nonn %O A347873 1,2 %A A347873 _Antti Karttunen_, Sep 17 2021