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 A127681 #14 Nov 16 2021 03:42:16
%S A127681 1,1,2,4,9,19,42,90,198,428,936,2030,4430,9626,20978,45622,99367,
%T A127681 216197,470736,1024420,2230183,4853881,10566170,22997974,50061240,
%U A127681 108964596,237186018,516272178,1123772192,2446081048,5324371354,11589437278
%N A127681 a(0) = 1. a(n+1) = sum{k=0 to n} a(n-k)*a(ceiling(k/2)).
%H A127681 Robert Israel, <a href="/A127681/b127681.txt">Table of n, a(n) for n = 0..2958</a>
%F A127681 a(n) ~ c * d^n, where d = 2.17668434612191638687360948440303534082431658053308188275404767951385648... and c = 0.39120452795484998747876543545867360129596245925827624710922741574667... - _Vaclav Kotesovec_, Nov 16 2021
%p A127681 f:= proc(n) option remember;
%p A127681 add(procname(n-1-k)*procname(ceil(k/2)),k=0..n-1)
%p A127681 end proc:
%p A127681 f(0):= 1:
%p A127681 map(f, [$0..40]); # _Robert Israel_, Feb 16 2018
%t A127681 f[l_List] := Block[{n = Length[l] - 1},Append[l, Sum[l[[n - k + 1]]*l[[Ceiling[k/2] + 1]], {k, 0, n}]]];Nest[f, {1}, 32] (* _Ray Chandler_, Feb 13 2007 *)
%Y A127681 Cf. A127680.
%K A127681 easy,nonn
%O A127681 0,3
%A A127681 _Leroy Quet_, Jan 23 2007
%E A127681 Extended by _Ray Chandler_, Feb 13 2007