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 A307358 #14 Apr 04 2019 12:45:27
%S A307358 1,-4,72,-1345,27886,-610558,13861334,-322838475,7663363513,
%T A307358 -184598740512,4498935186891,-110693299767349,2745124008220296,
%U A307358 -68532209858173364,1720678086867077832,-43415209670536390089,1100146390869600888470
%N A307358 a(n) = Sum_{0<=i<=j<=k<=n} (-1)^(i+j+k) * (i+j+k)!/(i!*j!*k!).
%F A307358 a(n) ~ (-1)^n * 3^(3*n + 13/2) / (1792*Pi*n). - _Vaclav Kotesovec_, Apr 04 2019
%t A307358 Table[Sum[Sum[Sum[(-1)^(i+j+k) * (i+j+k)!/(i!*j!*k!), {i, 0, j}], {j, 0, k}], {k, 0, n}], {n, 0, 20}] (* _Vaclav Kotesovec_, Apr 04 2019 *)
%o A307358 (PARI) {a(n) = sum(i=0, n, sum(j=i, n, sum(k=j, n, (-1)^(i+j+k)*(i+j+k)!/(i!*j!*k!))))}
%Y A307358 Cf. A144660, A307318, A307352, A307354.
%K A307358 sign
%O A307358 0,2
%A A307358 _Seiichi Manyama_, Apr 04 2019