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 A129653 #12 Feb 21 2022 15:46:33
%S A129653 1,1,4,15,83,556,4435,40773,423836,4908403,62606297,871421976,
%T A129653 13136605577,213122669141,3701085673676,68480774296803,
%U A129653 1344611320542931,27917413103561540,611000785570868627,14056645627856206809,339081826905338009620,8557085279980716462407
%N A129653 Antidiagonal sums of number triangle A129652.
%H A129653 T.-X. He, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL11/He/he51.html">A symbolic operator approach to power series transformation-expansion formulas</a>, JIS 11 (2008) 08.2.7
%F A129653 a(n) = Sum_{k=0..floor(n/2)} (((n-k)!/k!)*sum{i=0..n-2k} C(n-2k-1,i)/(n-2k-i)!).
%o A129653 (PARI) a(n) = sum(k=0, n\2, ((n-k)!/k!)*sum(i=0, n-2*k, binomial(n-2*k-1,i)/(n-2*k-i)!)); \\ _Michel Marcus_, Sep 10 2015
%Y A129653 Cf. A129652.
%K A129653 easy,nonn
%O A129653 0,3
%A A129653 _Paul Barry_, Apr 26 2007