OFFSET
1,2
COMMENTS
Exponential reversion of the sum of divisors function (A000203).
MATHEMATICA
nmax = 18; CoefficientList[InverseSeries[Series[Sum[DivisorSigma[1, k] x^k/k!, {k, 1, nmax}], {x, 0, nmax}], x], x] Range[0, nmax]! // Rest
PROG
(PARI) seq(n)= Vec(serlaplace(serreverse(sum(k=1, n, sigma(k)*x^k/k!) + O(x*x^n)))) \\ Michel Marcus, Apr 22 2020
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Apr 22 2020
STATUS
approved