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 A300865 #6 Mar 14 2018 21:21:40
%S A300865 1,0,1,0,1,1,2,2,4,6,10,16,27,46,77,131,224,391,672,1180,2050,3626,
%T A300865 6344,11276,19863,35479,62828,112685,200462,360627,644199,1162296,
%U A300865 2083572,3768866,6777314,12289160,22158106,40255496,72765144,132453122,239936528,437445448
%N A300865 Signed recurrence over binary enriched p-trees: a(n) = (-1)^(n-1) + Sum_{x + y = n, 0 < x <= y < n} a(x) * a(y).
%t A300865 a[n_]:=a[n]=(-1)^(n-1)+Sum[a[k]*a[n-k],{k,1,n/2}];
%t A300865 Array[a,50]
%Y A300865 Cf. A000992, A001190, A007317, A063834, A099323, A196545, A220418, A273866, A273873, A289501, A290261, A300352, A300442, A300443, A300862, A300863, A300864, A300866.
%K A300865 nonn
%O A300865 1,7
%A A300865 _Gus Wiseman_, Mar 13 2018