A347877 - OEIS

A347877

Numbers k for which A003415(sigma(k)) is odd.

2, 4, 5, 9, 10, 13, 16, 17, 20, 25, 26, 29, 32, 34, 37, 40, 41, 45, 52, 53, 58, 61, 64, 68, 72, 73, 74, 80, 82, 89, 90, 97, 98, 101, 104, 106, 109, 113, 116, 117, 122, 128, 136, 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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Numbers k such that A342925(k) == 1 (mod 2).

Squares present in this sequence are terms of A347885 squared. (There are no even squares present, see A235991 for the explanation).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..20000

FORMULA

For all n >= 1, A349909(a(n)) = n. - Antti Karttunen, Feb 23 2022

MATHEMATICA

ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[234], OddQ[ad[DivisorSigma[1, #]]] &] (* Amiram Eldar, Sep 19 2021 *)

CROSSREFS

Cf. A000203, A003415, A023194 (subsequence), A235991, A342925, A347872, A347873, A347885, A347878 (complement).

Cf. A347870 (characteristic function), A349909 (its partial sums).

Sequence in context: A274693 A024618 A089221 * A167180 A091271 A063985

Adjacent sequences: A347874 A347875 A347876 * A347878 A347879 A347880

KEYWORD

nonn

AUTHOR

Antti Karttunen, Sep 19 2021

STATUS

approved