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 A308296 #25 May 24 2019 12:39:03
%S A308296 1,1,7,842,7958726,15467641899285,10893033763705794846727,
%T A308296 4247805448772073978048752721163278,
%U A308296 1299618941291522676629215597535104557826094801396,419715170056359079715862408734598208208707081189266290220651371206
%N A308296 a(n) = (1/n!) * Sum_{i_1=1..n} Sum_{i_2=1..n} ... Sum_{i_n=1..n} multinomial(i_1+i_2+...+i_n; i_1, i_2, ... , i_n).
%H A308296 Seiichi Manyama, <a href="/A308296/b308296.txt">Table of n, a(n) for n = 0..27</a>
%F A308296 a(n) = A144510(n,n).
%e A308296 a(2) = (1/2) * (binomial(1+1,1) + binomial(1+2,2) + binomial(2+1,1) + binomial(2+2,2)) = 7.
%o A308296 (PARI) {a(n) = sum(i=n, n^2, i!*polcoef(sum(j=1, n, x^j/j!)^n, i))/n!}
%Y A308296 Cf. A144510, A144512, A274762, A281901.
%K A308296 nonn
%O A308296 0,3
%A A308296 _Seiichi Manyama_, May 19 2019