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 A352901 #6 Apr 07 2022 12:10:30
%S A352901 1,2,3,6,15,36,80,172,369,796,1727,3774,8322,18528,41643,94460,216121,
%T A352901 498186,1155147,2689626,6278841,14676900,34316598,80194032,187195554,
%U A352901 436310190,1015176726,2357708258,5465611759,12647864454,29219750157,67403414568,155276809533
%N A352901 a(0) = 1; a(n) = Sum_{k=0..floor(n/3)} binomial(n+1,3*k+1) * a(k).
%C A352901 Self-convolution of A351970.
%F A352901 G.f. A(x) satisfies: A(x) = A(x^3/(1 - x)^3) / (1 - x)^2.
%F A352901 E.g.f.: d/dx ( exp(x) * Sum_{n>=0} a(n) * x^(3*n+1) / (3*n+1)! ).
%t A352901 a[0] = 1; a[n_] := a[n] = Sum[Binomial[n + 1, 3 k + 1] a[k], {k, 0, Floor[n/3]}]; Table[a[n], {n, 0, 32}]
%t A352901 nmax = 32; A[_] = 1; Do[A[x_] = A[x^3/(1 - x)^3]/(1 - x)^2 + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%Y A352901 Cf. A040027, A051163, A351970, A352902.
%K A352901 nonn
%O A352901 0,2
%A A352901 _Ilya Gutkovskiy_, Apr 07 2022