A307308 Self-composition of the Euler totient function (A000010).

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

Offset: 1

Author

Ilya Gutkovskiy, Apr 02 2019

Keywords

• nonn

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 1..500
• Eric Weisstein's World of Mathematics, Totient Function

Crossrefs

Cf. A000010, A008683, A010554, A065093, A307309.

Programs

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}]

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.