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 A307875 #6 May 02 2019 16:06:41
%S A307875 1,1,1,3,8,23,78,308,1343,6288,31520,169556,976219,5974381,38597158,
%T A307875 262016556,1864047379,13870571346,107732190252,871392244426,
%U A307875 7323432971279,63823847508765,575833492837041,5370836704825787,51720220231890625,513595474725399215,5253091234710411001
%N A307875 G.f. A(x) satisfies: A(x) = 1 + x*(1 + x*A(x/(1 - x)^2)/(1 - x)^2).
%F A307875 Recurrence: a(n+1) = Sum_{k=0..n} binomial(n+k,2*k+1)*a(k).
%t A307875 terms = 26; A[_] = 0; Do[A[x_] = 1 + x (1 + x A[x/(1 - x)^2]/(1 - x)^2) + O[x]^(terms + 1) // Normal, terms + 1]; CoefficientList[A[x], x]
%t A307875 a[n_] := a[n] = Sum[Binomial[n + k - 1, 2 k + 1] a[k], {k, 0, n - 1}]; a[0] = 1; a[1] = 1; Table[a[n], {n, 0, 26}]
%Y A307875 Cf. A000110, A007476, A040027.
%K A307875 nonn
%O A307875 0,4
%A A307875 _Ilya Gutkovskiy_, May 02 2019