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 A307305 #18 Feb 16 2025 08:33:55
%S A307305 1,4,12,34,92,246,640,1660,4264,10914,27732,70247,177466,447570,
%T A307305 1126344,2828465,7089391,17746456,44384884,110927184,276993616,
%U A307305 691007612,1722214602,4289021667,10675557184,26561494820,66063726382,164248795485,408168287028,1013819012498
%N A307305 Self-composition of the number of divisors function (A000005).
%H A307305 Vaclav Kotesovec, <a href="/A307305/b307305.txt">Table of n, a(n) for n = 1..760</a>
%H A307305 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DivisorFunction.html">Divisor Function</a>
%F A307305 G.f.: g(g(x)), where g(x) = Sum_{k>=1} x^k/(1 - x^k) is the g.f. of A000005.
%t A307305 g[x_] := g[x] = Sum[x^k/(1 - x^k), {k, 1, 30}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 30}]
%Y A307305 Cf. A000005, A010553, A055507, A307306.
%K A307305 nonn
%O A307305 1,2
%A A307305 _Ilya Gutkovskiy_, Apr 01 2019