OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(1) = 1; a(n > 1) = Sum_{d = 1..n-1} a(d) * floor(n/d-1).
G.f. A(x) satisfies A(x) = x + (1/(1 - x)) * Sum_{k>=2} A(x^k). - Ilya Gutkovskiy, Sep 06 2019
MATHEMATICA
sau[n_]:=If[n==1, 1, Sum[sau[d], {k, n}, {d, Most[Divisors[k]]}]];
Table[sau[n], {n, 30}]
PROG
(Python)
from functools import lru_cache
@lru_cache(maxsize=None)
def A320225(n): return 1 if n == 1 else sum(A320225(d)*(n//d-1) for d in range(1, n)) # Chai Wah Wu, Jun 08 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 07 2018
STATUS
approved