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 A144662 #12 Apr 04 2019 04:33:03
%S A144662 0,1,266,45296,7958726,1495388159,295887993624,60790021361170,
%T A144662 12845435390707724,2774049143394729653,609542744597785306189,
%U A144662 135840016223787254538508,30629983532857972983331740,6975352854342057056747327899,1602003695575764851150428242804,370631496919828403109950449644134
%N A144662 a(n) = Sum_{i=1..n} Sum_{j=1..n} Sum_{k=1..n} Sum_{l=1..n} (i+j+k+l)!/(4!*i!*j!*k!*l!).
%H A144662 Moa Apagodu, David Applegate, N. J. A. Sloane, and Doron Zeilberger, <a href="http://arxiv.org/abs/1701.08394">Analysis of the Gift Exchange Problem</a>, arXiv:1701.08394, 2017.
%H A144662 David Applegate and N. J. A. Sloane, <a href="http://arxiv.org/abs/0907.0513">The Gift Exchange Problem</a> (arXiv:0907.0513, 2009)
%p A144662 f:=n->add( add( add( add( (i+j+k+l)!/(4!*i!*j!*k!*l!), i=1..n),j=1..n),k=1..n),l=1..n); [seq(f(n),n=0..16)];
%t A144662 a[n_] := Sum[(i+j+k+l)!/(4! i! j! k! l!), {i, n}, {j, n}, {k, n}, {l, n}];
%t A144662 Table[a[n], {n, 0, 15}] (* _Jean-François Alcover_, Sep 05 2018 *)
%t A144662 Table[(Binomial[2*n + 2, n + 1] - 2*(1 + n) + Sum[(1 + k + l + 2*n)! HypergeometricPFQ[{1, -1 - k - l - n, -n}, {-1 - k - l - 2*n, -k - l - n}, 1]/((1 + k + l + n) k! l! (n!)^2) - (2*(1 + k + l + n)!)/((1 + k + l) k! l! n!), {k, 1, n}, {l, 1, n}])/24, {n, 0, 15}] (* _Vaclav Kotesovec_, Apr 04 2019 *)
%Y A144662 Column 4 of A144512. Cf. A144660, A144661.
%K A144662 nonn
%O A144662 0,3
%A A144662 _N. J. A. Sloane_, Feb 01 2009