login
A333957
E.g.f. A(x) satisfies: A(x) = x - Sum_{k>=2} sigma(k) * A(x)^k / k!.
1
1, -3, 23, -292, 5194, -118879, 3327092, -110077602, 4202995203, -181898058107, 8799087726483, -470477273391491, 27552899058423712, -1753972172620598718, 120590533350099961096, -8905268067453051058302, 702994242229769687066025, -59076500305914641133294712
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