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 A307350 #20 May 20 2019 15:25:34
%S A307350 0,1,-5,120,-2380,52556,-1192625,27798310,-660128942,15907062666,
%T A307350 -387785597485,9543399745815,-236715891871160,5910596888393926,
%U A307350 -148421725618783545,3745355227481531010,-94917946415633366050,2414582011729590475886
%N A307350 a(n) = -Sum_{i=1..n} Sum_{j=1..n} Sum_{k=1..n} (-1)^(i+j+k) * (i+j+k)!/(3!*i!*j!*k!).
%H A307350 Seiichi Manyama, <a href="/A307350/b307350.txt">Table of n, a(n) for n = 0..100</a>
%F A307350 a(n) ~ -(-1)^n * 3^(3*n + 5/2) / (256*Pi*n). - _Vaclav Kotesovec_, Apr 04 2019
%t A307350 Table[-Sum[Sum[Sum[(-1)^(i + j + k)*(i + j + k)!/(3!*i!*j!*k!), {i, 1, n}], {j, 1, n}], {k, 1, n}], {n, 0, 17}] (* _Amiram Eldar_, Apr 03 2019 *)
%o A307350 (PARI) {a(n) = -sum(i=1, n, sum(j=1, n, sum(k=1, n, (-1)^(i+j+k)*(i+j+k)!/(6*i!*j!*k!))))}
%o A307350 (PARI) {a(n) = -sum(i=3, 3*n, (-1)^i*i!*polcoef(sum(j=1, n, x^j/j!)^3, i))/6} \\ _Seiichi Manyama_, May 20 2019
%Y A307350 Cf. A144511, A307318, A307349, A307351.
%K A307350 sign
%O A307350 0,3
%A A307350 _Seiichi Manyama_, Apr 03 2019