OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..149
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
FORMULA
a(n) = Sum_{j=0..n} (-6)^j*binomial(n,j)*(3*n-3*j)!.
MAPLE
a:=n->sum((-6)^i*binomial(n, i)*(3*n-3*i)!, i=0..n).
MATHEMATICA
Table[Sum[(-6)^i*Binomial[n, i]*(3*n - 3*i)!, {i, 0, n}], {n, 1, 20}] (* G. C. Greubel, May 11 2019 *)
PROG
(PARI) {a(n) = sum(j=0, n, (-6)^j*binomial(n, j)*(3*(n-j))!)}; \\ G. C. Greubel, May 11 2019
(Magma) [(&+[(-6)^j*Binomial(n, j)*Factorial(3*n-3*j): j in [0..n]]): n in [1..20]]; // G. C. Greubel, May 11 2019
(Sage) [sum((-6)^j*binomial(n, j)*factorial(3*n-3*j) for j in (0..n)) for n in (1..20)] # G. C. Greubel, May 11 2019
(GAP) List([1..20], n-> Sum([0..n], j-> (-6)^j*Binomial(n, j)* Factorial(3*n-3*j))) # G. C. Greubel, May 11 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Milan Janjic, Apr 09 2007
STATUS
approved