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 A089976 #12 Mar 21 2023 07:38:35 %S A089976 1,1,2,4,8,20,52,146,458,1498,5240,19562,76006,311258,1334108,5931250, %T A089976 27492122,132096626,655783888,3368747018,17837850110,97228103482, %U A089976 545514383396,3142793126018,18578114240578,112620106745570,698987455899992,4439420959115866,28832596784976998,191284437539842538 %N A089976 Antidiagonal sums of array A089975. %o A089976 (PARI) T(n, k) = sum(i=max(0,n-k), floor(n/2), n!*k!/(2^i*(n-2*i)!*(k-n+i)!*i!)); \\ A089975 %o A089976 a(n) = sum(i=0, n, T(i, n-i)); \\ _Michel Marcus_, Mar 21 2023 %Y A089976 Cf. A089975. %K A089976 easy,nonn %O A089976 0,3 %A A089976 _Paul Boddington_, Nov 17 2003 %E A089976 Name edited and more terms from _Michel Marcus_, Mar 21 2023