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

1,2

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.

Links

Table of n, a(n) for n=1..77.

Mathematica

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

Prog

(PARI) isA347878(n) = !A347870(n);

Crossrefs

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

Positions of zeros in A347870.

Sequence in context: A155932 A298980 A206586 * A289176 A277851 A047557

Adjacent sequences: A347875 A347876 A347877 * A347879 A347880 A347881

Keyword

nonn

Author

Antti Karttunen, Sep 19 2021

Status

approved