OFFSET
1,2
COMMENTS
FORMULA
(Sum_{j=1..k} sigma_2(j)) mod k = A064602(k) mod k = 0.
EXAMPLE
Summing divisor-square sums for j = 1..8 gives 1+5+10+21+26+50+50+85 = 248, which is divisible by 8, so 8 is a term and the integer quotient is 31.
MATHEMATICA
k = 1; lst = {}; s = 0; While[k < 1000000001, s = s + DivisorSigma[2, k]; If[ Mod[s, k] == 0, AppendTo[lst, k]; Print@ k]; k++]; lst (* Robert G. Wilson v, Apr 25 2011 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Sep 24 2001
EXTENSIONS
a(15)-a(19) from Donovan Johnson, Jun 21 2010
a(20) from Amiram Eldar, Jan 18 2024
STATUS
approved