A069520 - OEIS

%I #15 May 14 2022 11:30:49

%S 1,39,793,1638,2379,2394,7137,8190,11970,14274,18135,19530,30927,

%T 31122,35685,36270,50700,61854,71370,76921,81900,92781,99918,119700,

%U 154635,155610,185562,195300,230763,253890,269500,299754,304038,309270

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

%C 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

%H Amiram Eldar, <a href="/A069520/b069520.txt">Table of n, a(n) for n = 1..500</a>

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

%o (PARI) is_A069520(n)=!(sumdiv(n,d,d*sigma(d))%n) \\ - _M. F. Hasler_, Nov 24 2013

%Y Cf. A000203, A232067, A232354.

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, Apr 16 2002