This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A307309 #6 Feb 16 2025 08:33:55
%S A307309 1,6,26,99,348,1194,4000,13326,44058,144066,462504,1459194,4545588,
%T A307309 14068554,43450848,134213808,414692130,1280610858,3948172380,
%U A307309 12142365042,37235047770,113844652986,347103133068,1055610536520,3202944247674,9697395164616,29298206343284
%N A307309 Self-composition of the Dedekind psi function (A001615).
%H A307309 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DedekindFunction.html">Dedekind Function</a>
%F A307309 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 A307309 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 A307309 Cf. A001615, A008683, A307308.
%K A307309 nonn
%O A307309 1,2
%A A307309 _Ilya Gutkovskiy_, Apr 02 2019