A347873 Numbers k such that k and A003415(sigma(k)) are of different parity.

1, 2, 3, 4, 7, 10, 11, 15, 16, 19, 20, 21, 23, 26, 27, 31, 32, 33, 34, 35, 39, 40, 43, 47, 49, 51, 52, 55, 57, 58, 59, 63, 64, 65, 67, 68, 69, 71, 72, 74, 75, 77, 79, 80, 81, 82, 83, 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

Offset: 1

Author

Antti Karttunen, Sep 17 2021

Keywords

• nonn

Comments

Numbers k for which A347870(k) differs from A000035(k).

Crossrefs

Cf. A000035, A000203, A003415, A342925, A347870.

Positions of ones in A347871 (the characteristic function). A347872 gives the complement.

Programs

Mathematica

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 *)