OFFSET
1,15
COMMENTS
The Euler transform of a sequence q is the sequence of coefficients of x^n, n > 0, in the expansion of Product_{n > 0} 1/(1 - x^n)^q(n).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..5000
OEIS Wiki, Euler transform
MAPLE
# The function EulerInvTransform is defined in A358451.
a := EulerInvTransform(n -> ifelse(n=0, 1, NumberTheory:-SumOfDivisors(n, 0))):
seq(a(n), n = 1..64); # Peter Luschny, Nov 21 2022
MATHEMATICA
EulerInvTransform[{}]={}; EulerInvTransform[seq_]:=Module[{final={}}, For[i=1, i<=Length[seq], i++, AppendTo[final, i*seq[[i]]-Sum[final[[d]]*seq[[i-d]], {d, i-1}]]];
Table[Sum[MoebiusMu[i/d]*final[[d]], {d, Divisors[i]}]/i, {i, Length[seq]}]];
EulerInvTransform[Table[DivisorSigma[0, n], {n, 100}]]
PROG
(Python)
from functools import lru_cache
from sympy import mobius, divisors, divisor_count
def A320779(n):
@lru_cache(maxsize=None)
def b(n): return divisor_count(n)
@lru_cache(maxsize=None)
def c(n): return n*b(n)-sum(c(k)*b(n-k) for k in range(1, n))
return sum(mobius(d)*c(n//d) for d in divisors(n, generator=True))//n # Chai Wah Wu, Jul 15 2024
CROSSREFS
KEYWORD
sign
AUTHOR
Gus Wiseman, Oct 22 2018
STATUS
approved