OFFSET
1,3
FORMULA
G.f.: Sum_{k>=1} tau(k) * x^(2*k) / (1 - x^k)^2. - Ilya Gutkovskiy, Aug 19 2021
MATHEMATICA
Table[DivisorSum[n, (#-1)DivisorSigma[0, n/#]&], {n, 100}] (* Giorgos Kalogeropoulos, Aug 19 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d-1)*numdiv(n/d)) \\ Michel Marcus, Jun 17 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, May 04 2002
STATUS
approved