OFFSET
1,2
FORMULA
a(n) ~ n^n / (sqrt(1 + LambertW(exp(-1))) * exp(n) * LambertW(exp(-1))^n).
MATHEMATICA
Table[Sum[Binomial[n, k] * DivisorSigma[n, k], {k, 1, n}], {n, 1, 20}]
PROG
(PARI) {a(n)=sum(k=1, n, binomial(n, k)*sigma(k, n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Oct 25 2024
STATUS
approved