A123385 a(n) = (n!)^2/2.

2, 18, 288, 7200, 259200, 12700800, 812851200, 65840947200, 6584094720000, 796675461120000, 114721266401280000, 19387894021816320000, 3800027228275998720000, 855006126362099712000000

Offset

2,1

Links

G. C. Greubel, Table of n, a(n) for n = 2..250

Formula

a(n) = Sum[Product[k, {k, i, n}]*a(i), {i, 0, n - 1}].

Mathematica

f[0] = 0; f[1] = 1; f[n_] := f[n] = Sum[Product[k, {k, i, n}]*f[i], {i, 0, n - 1}] Table[f[n], {n, 0, 30}]
Table[(n!)^2/2, {n, 2, 50}] (* G. C. Greubel, Oct 13 2017 *)

Prog

(PARI) for(n=2, 25, print1((n!)^2/2, ", ")) \\ G. C. Greubel, Oct 13 2017
(Magma) [(Factorial(n))^2/2: n in [2..25]]; // G. C. Greubel, Oct 13 2017

Crossrefs

Sequence in context: A127134 A131455 A084947 * A374086 A121564 A224384

Adjacent sequences: A123382 A123383 A123384 * A123386 A123387 A123388

Keyword

nonn

Author

Gary W. Adamson, Oct 13 2006

Status

approved