A069520 Numbers k such that (1/k) * Sum_{d|k} d*sigma(d) is an integer.

1, 39, 793, 1638, 2379, 2394, 7137, 8190, 11970, 14274, 18135, 19530, 30927, 31122, 35685, 36270, 50700, 61854, 71370, 76921, 81900, 92781, 99918, 119700, 154635, 155610, 185562, 195300, 230763, 253890, 269500, 299754, 304038, 309270

Offset: 1

Author

Benoit Cloitre, Apr 16 2002

Keywords

• easy
• nonn

Comments

Sequence A232354 starts in a very similar way, and the two sequences have a common subsequence A232067 = (1, 39, 793, 2379, 7137, 76921, 230763, ...), but neither is a subsequence of the other. - M. F. Hasler, Nov 24 2013

Links

• Amiram Eldar, Table of n, a(n) for n = 1..500

Crossrefs

Cf. A000203, A232067, A232354.

Programs

Mathematica

s[n_] := DivisorSum[n, # * DivisorSigma[1, #] &]; Select[Range[300000], Divisible[s[#], #] &] (* Amiram Eldar, May 14 2022 *)

PARI

is_A069520(n)=!(sumdiv(n,d,d*sigma(d))%n) \\ - M. F. Hasler, Nov 24 2013