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 A226391 #28 Sep 01 2022 05:00:52
%S A226391 1,2,9,103,2073,58481,2101813,91492906,4671050401,273437232283,
%T A226391 18046800575211,1325445408799007,107200425419863009,
%U A226391 9466283137384124247,906151826270369213655,93459630239922214535911,10331984296666203358431361,1218745075041575200343722415
%N A226391 a(n) = Sum_{k=0..n} binomial(k*n, k).
%H A226391 Vincenzo Librandi, <a href="/A226391/b226391.txt">Table of n, a(n) for n = 0..100</a>
%F A226391 a(n) ~ binomial(n^2, n).
%t A226391 Table[Sum[Binomial[k*n, k], {k, 0, n}], {n, 0, 20}]
%o A226391 (Maxima) A226391(n):=sum(binomial(k*n,k), k,0,n); makelist(A226391(n),n,0,30); /* _Martin Ettl_, Jun 06 2013 */
%o A226391 (Magma) [(&+[Binomial(n*j,j): j in [0..n]]): n in [0..30]]; // _G. C. Greubel_, Aug 31 2022
%o A226391 (SageMath)
%o A226391 @CachedFunction
%o A226391 def A226391(n): return sum(binomial(n*j, j) for j in (0..n))
%o A226391 [A226391(n) for n in (0..30)] # _G. C. Greubel_, Aug 31 2022
%Y A226391 Cf. A072034, A086331, A096131, A167008, A167010, A349471.
%K A226391 nonn
%O A226391 0,2
%A A226391 _Vaclav Kotesovec_, Jun 06 2013