OFFSET
0,2
FORMULA
a(n) ~ (-1)^n * 3^(3*n + 13/2) / (1792*Pi*n). - Vaclav Kotesovec, Apr 04 2019
MATHEMATICA
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 *)
PROG
(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!))))}
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Apr 04 2019
STATUS
approved