A110348 a(2) = 1 by definition; otherwise a(n) = A109347(n)/n.

1, 1, 8, 45, 504, 5040, 86400, 1247400, 28828800, 544864320, 15850598400, 370507737600, 12996271411200, 362038989312000, 14867734494412800, 480878287553664000, 22629566473113600000, 833522365093017600000

Offset: 1

Author

Amarnath Murthy, Jul 21 2005

Keywords

• easy
• nonn

Examples

			a(3) = 2*3*4/3 = 8, a(6)= 3*4*5*7*8*9/6 = 5040.
		

Crossrefs

Cf. A110347.

Formula

a(2n+1) = (n+1)(n+2)...(2n-1)(2n)(2n+2) ...(3n+1)(3n+2). a(2n) = (1/2)(n+1)(n+2)...(2n-2)(2n-1)(2n+1)(2n+2)...(3n-1)(3n).

Extensions

More terms from Joshua Zucker, May 08 2006