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 A331519 #5 Jan 19 2020 09:20:04
%S A331519 1,1,1,3,3,9,15,63,63,189,315,1323,1701,6237,12285,59535,59535,178605,
%T A331519 297675,1250235,1607445,5893965,11609325,56260575,63761985,213790185,
%U A331519 393824025,1811590515,2531725875,10025634465,21210236775,109876902975,109876902975,329630708925
%N A331519 a(0) = 1; a(n) = Sum_{k=1..n} (binomial(n,k) mod 2) * a(k-1) * a(n-k).
%t A331519 a[0] = 1; a[n_] := a[n] = Sum[Mod[Binomial[n, k], 2] a[k - 1] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 33}]
%Y A331519 Cf. A000108, A001147, A047749, A047999, A062177, A166966.
%K A331519 nonn
%O A331519 0,4
%A A331519 _Ilya Gutkovskiy_, Jan 19 2020