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 A376113 #5 Sep 11 2024 00:45:04
%S A376113 1,1,6,137,11938,4095882,5599192492,30588428274345,668265444025582410,
%T A376113 58395039572032120897838,20410643002515607839683651348,
%U A376113 28536181214271796693200339702494058,159585939576145805663910944364491926768148,3569877304419418296304606194938539586766279745396
%N A376113 a(0) = 1; a(n) = (1/3) * Sum_{k=1..n} (4^k-1) * a(k-1) * a(n-k).
%F A376113 G.f. A(x) satisfies: A(x) = 3 / (3 + x * A(x) - 4 * x * A(4*x)).
%t A376113 a[0] = 1; a[n_] := a[n] = (1/3) Sum[(4^k - 1) a[k - 1] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 13}]
%t A376113 nmax = 13; A[_] = 0; Do[A[x_] = 3/(3 + x A[x] - 4 x A[4 x]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%Y A376113 Cf. A015085, A337556, A376111, A376112.
%K A376113 nonn
%O A376113 0,3
%A A376113 _Ilya Gutkovskiy_, Sep 10 2024