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%I #9 Sep 18 2021 22:04:43
%S 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 49,51,52,55,57,58,59,63,64,65,67,68,69,71,72,74,75,77,79,80,81,82,83,
%U 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 Numbers k such that k and A003415(sigma(k)) are of different parity.
%C Numbers k for which A347870(k) differs from A000035(k).
%t 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 Cf. A000035, A000203, A003415, A342925, A347870.
%Y Positions of ones in A347871 (the characteristic function). A347872 gives the complement.
%K nonn
%O 1,2
%A _Antti Karttunen_, Sep 17 2021