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 A302356 #4 Apr 06 2018 17:28:53
%S A302356 1,8,123,3064,107355,4880896,273564907,18252720536,1413701944431,
%T A302356 124714304306536,12347969626724127,1356049318451627812,
%U A302356 163596640499821625005,21508738592360523314552,3060986664449504902865167,468816798653492762623354936,76889830949170048691162162275
%N A302356 a(n) = coefficient of x^n in the n-th iteration (n-fold self-composition) of the g.f. of squares (A000290).
%H A302356 N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>
%H A302356 <a href="/index/Pol#polygonal_numbers">Index to sequences related to polygonal numbers</a>
%e A302356 The initial coefficients of successive iterations of g.f. A(x) = x*(1 + x)/(1 - x)^3 are as follows:
%e A302356 n = 1: 0, (1), 4, 9, 16, 25, ... g.f. A(x)
%e A302356 n = 2: 0, 1, (8), 50, 276, 1397, ... g.f. A(A(x))
%e A302356 n = 3: 0, 1, 12, (123), 1164, 10420, ... g.f. A(A(A(x)))
%e A302356 n = 4: 0, 1, 16, 228, (3064), 39542, ... g.f. A(A(A(A(x))))
%e A302356 n = 5: 0, 1, 20, 365, 6360, (107355), ... g.f. A(A(A(A(A(x)))))
%t A302356 Table[SeriesCoefficient[Nest[Function[x, x (1 + x)/(1 - x)^3], x, n], {x, 0, n}], {n, 17}]
%Y A302356 Cf. A000290, A030279, A119821, A302355.
%K A302356 nonn
%O A302356 1,2
%A A302356 _Ilya Gutkovskiy_, Apr 06 2018