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

1,2

Comments

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

Links

Table of n, a(n) for n=1..75.

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 *)

Crossrefs

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

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

Sequence in context: A266510 A266540 A342790 * A366567 A139759 A030292

Adjacent sequences: A347870 A347871 A347872 * A347874 A347875 A347876

Keyword

nonn

Author

Antti Karttunen, Sep 17 2021

Status

approved