OFFSET
1,1
FORMULA
a(n) ~ 2*zeta(3)*n^3.
MATHEMATICA
Accumulate[Table[DivisorSigma[1, k] * DivisorSigma[1, 2*k], {k, 1, 100}]]
PROG
(PARI) a(n) = sum(k=1, n, sigma(k)*sigma(2*k)); \\ Michel Marcus, Aug 18 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Aug 18 2021
STATUS
approved