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 A108469 #17 Jul 18 2021 11:28:30
%S A108469 1,1,2,4,9,20,45,100,220,478,1025,2169,4534,9364,19125,38646,77306,
%T A108469 153173,300765,585518,1130612,2166284,4120062,7780817,14595364,
%U A108469 27201794,50383690,92768457,169835952,309223286,560036477,1009124256
%N A108469 Main diagonal of A090806.
%D A108469 Alter, Ronald; Curtz, Thaddeus B.; Wang, Chung C. Permutations with fixed index and number of inversions. Proceedings of the Fifth Southeastern Conference on Combinatorics, Graph Theory and Computing (Florida Atlantic Univ., Boca Raton, Fla., 1974), pp. 209-228. Congressus Numerantium, No. X, Utilitas Math., Winnipeg, Man., 1974.
%H A108469 Vaclav Kotesovec, <a href="/A108469/b108469.txt">Table of n, a(n) for n = 0..90</a>
%t A108469 nmax = 20; p = 1; Do[Do[p = Expand[p*(1 - x^i*y^j)]; p = Select[p, (Exponent[#, x] <= nmax) && (Exponent[#, y] <= nmax) &], {i, 1, nmax}], {j, 1, nmax}]; p = Expand[Normal[Series[1/p, {x, 0, nmax}, {y, 0, nmax}]]]; p = Select[p, Exponent[#, x] == Exponent[#, y] &]; Flatten[{1, Table[Coefficient[p, x^n*y^n], {n, 1, nmax}]}] (* _Vaclav Kotesovec_, Apr 08 2016 *)
%K A108469 nonn
%O A108469 0,3
%A A108469 _Christian G. Bower_, Jun 03 2005