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 A099240 #9 Mar 09 2021 07:33:16
%S A099240 1,2,8,41,250,1757,13917,122166,1173662,12222605,136927351,1639768418,
%T A099240 20880556880,281460326864,4000651782511,59761935358025,
%U A099240 935445106491702,15303039199768237,261030618751031385,4632889302298054713
%N A099240 Main diagonal of A099239.
%H A099240 G. C. Greubel, <a href="/A099240/b099240.txt">Table of n, a(n) for n = 0..490</a>
%F A099240 a(n) = Sum_{j=0..n} binomial(n^2 - (n-1)*(j-1), j).
%F A099240 a(n) = Sum_{j=0..n} binomial(n + (n-1)*(j+1), n*(j+1) - 1) with a(0) = 1.
%t A099240 Table[Sum[Binomial[n^2 -(n-1)*(j-1), j], {j,0,n}], {n,0,30}] (* _G. C. Greubel_, Mar 09 2021 *)
%o A099240 (Sage) [sum(binomial(n^2 -(n-1)*(j-1), j) for j in (0..n)) for n in (0..30)] # _G. C. Greubel_, Mar 09 2021
%o A099240 (Magma) [1] cat [(&+[Binomial(n+(n-1)*(j+1), n*(j+1)-1): j in [0..n]]): n in [1..30]]; // _G. C. Greubel_, Mar 09 2021
%Y A099240 Cf. A099239.
%K A099240 easy,nonn
%O A099240 0,2
%A A099240 _Paul Barry_, Oct 08 2004