A347878 Numbers k for which A003415(sigma(k)) is even.

1, 3, 6, 7, 8, 11, 12, 14, 15, 18, 19, 21, 22, 23, 24, 27, 28, 30, 31, 33, 35, 36, 38, 39, 42, 43, 44, 46, 47, 48, 49, 50, 51, 54, 55, 56, 57, 59, 60, 62, 63, 65, 66, 67, 69, 70, 71, 75, 76, 77, 78, 79, 81, 83, 84, 85, 86, 87, 88, 91, 92, 93, 94, 95, 96, 99, 100, 102, 103, 105, 107, 108, 110, 111, 112, 114, 115

Offset: 1

Author

Antti Karttunen, Sep 19 2021

Keywords

• nonn

Comments

Numbers k such that A342925(k) == 0 (mod 2).

Odd squares present are terms of A347886 squared.

Conjecture: A342923 is a subsequence of this sequence. See comments in A347870.

Crossrefs

Cf. A000203, A003415, A342923, A342925, A347872, A347873, A347877 (complement), A347886.

Positions of zeros in A347870.

Programs

Mathematica

ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[115], EvenQ[ad[DivisorSigma[1, #]]] &] (* Amiram Eldar, Sep 19 2021 *)

PARI

isA347878(n) = !A347870(n);