A212805 a(n) = (1-(n-1)/2^n)*(n!)^n.

2, 1, 3, 162, 269568, 21772800000, 128430157824000000, 78734235726376796160000000, 6793969131008738346811156070400000000, 107405833909078014660339510303458240495616000000000, 392460917103771065568880570648836410770980864000000000000000000000, 407931390497527236736237611020825246476822200409679741237329920000000000000000000000

Offset: 0

Author

N. J. A. Sloane, May 27 2012

Keywords

• nonn

Links

• Morton Abramson, David Promislow, Enumeration of arrays by column rises, J. Combinatorial Theory Ser. A 24 (1978), no. 2, 247--250. MR0469773 (57 #9554).

Crossrefs

Cf. A212806.

Programs

Mathematica

Table[(1-(n-1)/2^n)(n!)^n,{n,0,15}] (* Harvey P. Dale, Dec 30 2023 *)

PARI

a(n) = (1-(n-1)/2^n)*(n!)^n; \\ Michel Marcus, Feb 27 2018