OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..386
FORMULA
a(n) = Sum_{k=1..n} Sum_{d|k} sigma_d(d).
G.f.: (1/(1-x)) * Sum_{k>=1} sigma_k(k) * x^k/(1 - x^k).
a(n) ~ n^n. - Vaclav Kotesovec, Aug 07 2022
MATHEMATICA
Table[Sum[DivisorSigma[k, k]Floor[n/k], {k, n}], {n, 20}] (* Harvey P. Dale, Sep 08 2024 *)
PROG
(PARI) a(n) = sum(k=1, n, sigma(k, k)*(n\k));
(PARI) a(n) = sum(k=1, n, sumdiv(k, d, sigma(d, d)));
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, sigma(k, k)*x^k/(1-x^k))/(1-x))
(Python)
from sympy import divisor_sigma
def A356079(n): return n+sum(divisor_sigma(k, k)*(n//k) for k in range(2, n+1)) # Chai Wah Wu, Jul 25 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 25 2022
STATUS
approved