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%I #16 Feb 25 2022 17:02:49
%S 2,4,5,9,10,13,16,17,20,25,26,29,32,34,37,40,41,45,52,53,58,61,64,68,
%T 72,73,74,80,82,89,90,97,98,101,104,106,109,113,116,117,122,128,136,
%U 137,146,148,149,153,157,160,162,164,173,178,180,181,193,194,196,197,200,202,208,212,218,226,229,232,233,234
%N Numbers k for which A003415(sigma(k)) is odd.
%C Numbers k such that A342925(k) == 1 (mod 2).
%C Squares present in this sequence are terms of A347885 squared. (There are no even squares present, see A235991 for the explanation).
%H Antti Karttunen, <a href="/A347877/b347877.txt">Table of n, a(n) for n = 1..20000</a>
%F For all n >= 1, A349909(a(n)) = n. - _Antti Karttunen_, Feb 23 2022
%t ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[234], OddQ[ad[DivisorSigma[1, #]]] &] (* _Amiram Eldar_, Sep 19 2021 *)
%Y Cf. A000203, A003415, A023194 (subsequence), A235991, A342925, A347872, A347873, A347885, A347878 (complement).
%Y Cf. A347870 (characteristic function), A349909 (its partial sums).
%K nonn
%O 1,1
%A _Antti Karttunen_, Sep 19 2021
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