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%I #13 Apr 23 2020 04:24:27
%S 1,-3,23,-292,5194,-118879,3327092,-110077602,4202995203,
%T -181898058107,8799087726483,-470477273391491,27552899058423712,
%U -1753972172620598718,120590533350099961096,-8905268067453051058302,702994242229769687066025,-59076500305914641133294712
%N E.g.f. A(x) satisfies: A(x) = x - Sum_{k>=2} sigma(k) * A(x)^k / k!.
%C Exponential reversion of the sum of divisors function (A000203).
%H <a href="/index/Res#revert">Index entries for reversions of series</a>
%t nmax = 18; CoefficientList[InverseSeries[Series[Sum[DivisorSigma[1, k] x^k/k!, {k, 1, nmax}], {x, 0, nmax}], x], x] Range[0, nmax]! // Rest
%o (PARI) seq(n)= Vec(serlaplace(serreverse(sum(k=1, n, sigma(k)*x^k/k!) + O(x*x^n)))) \\ _Michel Marcus_, Apr 22 2020
%Y Cf. A000203, A050390, A333956.
%K sign
%O 1,2
%A _Ilya Gutkovskiy_, Apr 22 2020
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