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A050392
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Exponential reversion of Euler totient function A000010.
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2
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1, -1, 1, 3, -39, 257, -909, -6389, 183715, -2326009, 15050003, 140089725, -6804608381, 130909360315, -1286161585477, -12952744700713, 970148927462835, -25588194678272039, 347909302401071797
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OFFSET
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1,4
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LINKS
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FORMULA
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E.g.f. A(x) satisfies: A(x) = x - Sum_{k>=2} phi(k) * A(x)^k / k!. - Ilya Gutkovskiy, Apr 22 2020
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MATHEMATICA
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length = 20; Range[length]! InverseSeries[Sum[EulerPhi[n] x^n/n!, {n, 1, length}] + O[x]^(length+1)][[3]] (* Vladimir Reshetnikov, Nov 07 2015 *)
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PROG
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(PARI) seq(n)= Vec(serlaplace(serreverse(sum(k=1, n, eulerphi(k)*x^k/k!) + O(x*x^n)))); \\ Michel Marcus, Apr 21 2020
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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