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 A119829 #4 Aug 26 2024 15:27:31
%S A119829 1,2,25,732,40681,3648990,480817681,87417943256,20966398997041,
%T A119829 6412838733766170,2436104066933508841,1125217445576328664692,
%U A119829 621010503476937955204825,403601732164215102065708342
%N A119829 Diagonal sum of number triangle A119828.
%F A119829 a(n)=sum{k=0..floor(n/2), (2(n-k))!/(2k)!}
%t A119829 Table[Sum[(2(n-k))!/(2k)!,{k,0,Floor[n/2]}],{n,0,20}] (* _Harvey P. Dale_, Aug 26 2024 *)
%K A119829 easy,nonn
%O A119829 0,2
%A A119829 _Paul Barry_, May 25 2006