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 A306280 #20 Feb 08 2019 04:05:58
%S A306280 1,3,26,416,9708,297662,11306572,512307336,26968496504,1617489748394,
%T A306280 108885682104744,8129721925098468,666736347200187804,
%U A306280 59582961423951290184,5762936296492591067968,599807329803134064385488,66843498592187788579795440
%N A306280 a(n) = Sum_{k=0..n} binomial(n,k)*binomial(n^2+k,k).
%H A306280 Seiichi Manyama, <a href="/A306280/b306280.txt">Table of n, a(n) for n = 0..337</a>
%F A306280 From _Vaclav Kotesovec_, Feb 08 2019: (Start)
%F A306280 a(n) ~ exp(1) * A135860(n).
%F A306280 a(n) ~ exp(n + 3/2) * n^(n - 1/2) / sqrt(2*Pi). (End)
%t A306280 a[n_] := Sum[Binomial[n,k] * Binomial[n^2+k,k], {k, 0, n}]; Array[a, 20, 0] (* _Amiram Eldar_, Feb 03 2019 *)
%o A306280 (PARI) {a(n) = sum(k=0, n, binomial(n, k)*binomial(n^2+k, k))}
%Y A306280 Cf. A001850, A114496, A135860, A156886, A156887.
%K A306280 nonn
%O A306280 0,2
%A A306280 _Seiichi Manyama_, Feb 02 2019