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 A307308 Self-composition of the Euler totient function (A000010). 2
 1, 2, 6, 15, 42, 106, 280, 702, 1778, 4398, 10910, 26678, 65172, 157656, 380524, 912846, 2185906, 5216588, 12433166, 29564544, 70189672, 166245574, 392909240, 926290066, 2178881218, 5114469170, 11985221654, 28049398284, 65588182636, 153277006212, 358073997608 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vaclav Kotesovec, Table of n, a(n) for n = 1..500 Eric Weisstein's World of Mathematics, Totient Function FORMULA G.f.: g(g(x)), where g(x) = Sum_{k>=1} mu(k)*x^k/(1 - x^k)^2 is the g.f. of A000010. MATHEMATICA g[x_] := g[x] = Sum[MoebiusMu[k] x^k/(1 - x^k)^2, {k, 1, 31}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 31}] CROSSREFS Cf. A000010, A008683, A010554, A065093, A307309. Sequence in context: A139379 A236110 A280782 * A065178 A178936 A221744 Adjacent sequences:  A307305 A307306 A307307 * A307309 A307310 A307311 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Apr 02 2019 STATUS approved

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Last modified January 26 10:40 EST 2020. Contains 331279 sequences. (Running on oeis4.)