A347880 Numbers k such that A342926(k) is a multiple of 3.

4, 5, 8, 14, 16, 20, 23, 25, 26, 30, 38, 41, 49, 51, 59, 62, 64, 66, 74, 77, 80, 86, 90, 92, 96, 102, 108, 113, 120, 122, 124, 127, 131, 134, 138, 143, 146, 149, 153, 158, 159, 164, 165, 167, 169, 174, 194, 196, 198, 200, 203, 204, 206, 209, 210, 213, 217, 218, 223, 236, 239, 243, 246, 254, 255, 257, 264, 267, 270

Offset

1,1

Links

Table of n, a(n) for n=1..69.

Mathematica

ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[270], Divisible[ad[DivisorSigma[1, #]] - #, 3] &] (* Amiram Eldar, Sep 18 2021 *)

Prog

(PARI)
A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));
A342926(n) = (A003415(sigma(n))-n);
isA347880(n) = !(A342926(n)%3);

Crossrefs

Positions of zeros in A347883.

Cf. A000203, A003415, A342926.

Cf. A005820, A342923 (subsequences).

Cf. also A347872.

Sequence in context: A242014 A145488 A050892 * A274167 A145265 A244161

Adjacent sequences: A347877 A347878 A347879 * A347881 A347882 A347883

Keyword

nonn

Author

Antti Karttunen, Sep 18 2021

Status

approved