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%I #19 Apr 22 2020 19:21:18
%S 1,-1,1,3,-39,257,-909,-6389,183715,-2326009,15050003,140089725,
%T -6804608381,130909360315,-1286161585477,-12952744700713,
%U 970148927462835,-25588194678272039,347909302401071797
%N Exponential reversion of Euler totient function A000010.
%H N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>
%H <a href="/index/Res#revert">Index entries for reversions of series</a>
%F E.g.f. A(x) satisfies: A(x) = x - Sum_{k>=2} phi(k) * A(x)^k / k!. - _Ilya Gutkovskiy_, Apr 22 2020
%t length = 20; Range[length]! InverseSeries[Sum[EulerPhi[n] x^n/n!, {n, 1, length}] + O[x]^(length+1)][[3]] (* _Vladimir Reshetnikov_, Nov 07 2015 *)
%o (PARI) seq(n)= Vec(serlaplace(serreverse(sum(k=1, n, eulerphi(k)*x^k/k!) + O(x*x^n)))); \\ _Michel Marcus_, Apr 21 2020
%Y Cf. A000010, A050391.
%K sign
%O 1,4
%A _Christian G. Bower_, Nov 15 1999
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