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 A351757 #5 Feb 19 2022 13:54:54
%S A351757 1,1,7,43,289,2239,19699,192025,2042971,23520715,291099349,3849621019,
%T A351757 54110928355,804827487493,12619011606775,207885167529523,
%U A351757 3587864566792753,64705561315720135,1216574535057705979,23797327657083197113,483390249416359706995
%N A351757 G.f. A(x) satisfies: A(x) = 1 + x * A(x/(1 - 3*x)) / (1 - 3*x)^2.
%F A351757 a(0) = 1; a(n) = Sum_{k=1..n} binomial(n,k-1) * 3^(k-1) * a(n-k).
%t A351757 nmax = 20; A[_] = 0; Do[A[x_] = 1 + x A[x/(1 - 3 x)]/(1 - 3 x)^2 + O[x]^(nmax + 1) // Normal,nmax + 1]; CoefficientList[A[x], x]
%t A351757 a[0] = 1; a[n_] := a[n] = Sum[Binomial[n, k - 1] 3^(k - 1) a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 20}]
%Y A351757 Cf. A004212, A040027, A255927, A351756.
%K A351757 nonn
%O A351757 0,3
%A A351757 _Ilya Gutkovskiy_, Feb 18 2022