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%I #5 Apr 02 2019 08:04:28
%S 1,6,26,99,348,1194,4000,13326,44058,144066,462504,1459194,4545588,
%T 14068554,43450848,134213808,414692130,1280610858,3948172380,
%U 12142365042,37235047770,113844652986,347103133068,1055610536520,3202944247674,9697395164616,29298206343284
%N Self-composition of the Dedekind psi function (A001615).
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DedekindFunction.html">Dedekind Function</a>
%F G.f.: g(g(x)), where g(x) = Sum_{k>=1} mu(k)^2*x^k/(1 - x^k)^2 is the g.f. of A001615.
%t g[x_] := g[x] = Sum[MoebiusMu[k]^2 x^k/(1 - x^k)^2, {k, 1, 27}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 27}]
%Y Cf. A001615, A008683, A307308.
%K nonn
%O 1,2
%A _Ilya Gutkovskiy_, Apr 02 2019
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