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 A307306 #16 Feb 16 2025 08:33:55
%S A307306 1,6,26,101,366,1294,4400,14706,48362,157583,507714,1621211,5138804,
%T A307306 16204008,50867068,159004142,494928072,1534638702,4743180908,
%U A307306 14622202326,44978845086,138074363360,422979847404,1293101281551,3945553307665,12018461150832,36556888102402
%N A307306 Self-composition of the sum of divisors function (A000203).
%H A307306 Vaclav Kotesovec, <a href="/A307306/b307306.txt">Table of n, a(n) for n = 1..750</a>
%H A307306 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DivisorFunction.html">Divisor Function</a>
%F A307306 G.f.: g(g(x)), where g(x) = Sum_{k>=1} k*x^k/(1 - x^k) is the g.f. of A000203.
%t A307306 g[x_] := g[x] = Sum[k x^k/(1 - x^k), {k, 1, 27}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 27}]
%Y A307306 Cf. A000203, A000385, A051027, A307305.
%K A307306 nonn
%O A307306 1,2
%A A307306 _Ilya Gutkovskiy_, Apr 01 2019