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%I #21 Feb 24 2024 01:12:24
%S 1,2,4,9,16,25,36,64,81,100,121,289,400,529,625,729,841,1024,1089,
%T 1296,1681,2025,2116,2209,2304,2401,2809,3025,3481,4096,5041,6724,
%U 6889,7569,7921,10201,11449,12769,13456,13924,15625,17161,18769,19881
%N Positive integers k such that the sum of the divisors of k, excluding 1, is a multiple of the number of divisors of k.
%C It appears that all terms except the second are squares. This has been verified for all terms less than one million.
%H Donovan Johnson, <a href="/A110878/b110878.txt">Table of n, a(n) for n = 1..1000</a>
%e The 9 divisors of 36 are {1,2,3,4,6,9,12,18,36}, giving sigma(36)-1=90, which is a multiple of 9. Thus 36 is a term of the sequence.
%t Select[Range[20000],Divisible[DivisorSigma[1,#]-1,DivisorSigma[0,#]]&] (* _Harvey P. Dale_, Dec 23 2020 *)
%K nonn
%O 1,2
%A _John W. Layman_, Sep 19 2005
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