OFFSET
1,2
FORMULA
a(n) = Sum_{k=1..n} Sum_{d|k} d!.
G.f.: (1/(1-x)) * Sum_{k>0} k! * x^k/(1 - x^k).
PROG
(PARI) a(n) = sum(k=1, n, n\k*k!);
(PARI) a(n) = sum(k=1, n, sumdiv(k, d, d!));
(PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, k!*x^k/(1-x^k))/(1-x))
(Python)
from math import factorial
def A355888(n): return factorial(n)+n+sum(factorial(k)*(n//k) for k in range(2, n)) if n>1 else 1 # Chai Wah Wu, Jul 21 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 20 2022
STATUS
approved