OFFSET
1,3
COMMENTS
Convolution of sigma with sigma_3.
In general, if k>=1, m>=1 and a(n) = Sum_{j=1..n-1} sigma_k(j) * sigma_m(n-j), then Sum_{j=1..n} a(j) ~ Gamma(k+1) * Gamma(m+1) * zeta(k+1) * zeta(m+1) * n^(k+m+2) / Gamma(k+m+3). - Vaclav Kotesovec, Sep 19 2024
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{k=1..n} a(k) ~ Pi^6 * n^6 / 64800. - Vaclav Kotesovec, Sep 19 2024
MATHEMATICA
Table[Sum[DivisorSigma[1, k] *DivisorSigma[3, n-k], {k, n-1}], {n, 36}] (* James C. McMahon, Aug 11 2024 *)
PROG
(Python)
from sympy import divisor_sigma
def A374963(n): return sum(divisor_sigma(i)*divisor_sigma(n-i, 3) for i in range(1, n))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Chai Wah Wu, Jul 25 2024
STATUS
approved