A129906 n!/(n^2) when an integer.

1, 20, 630, 4480, 36288, 3326400, 444787200, 5811886080, 81729648000, 19760412672000, 6082255020441600, 115852476579840000, 2322315553259520000, 1077167364120207360000, 24817936069329577574400, 596585001666576384000000, 14936720782466875392000000

Offset: 1

Author

Jonathan Vos Post, Jun 09 2007

Keywords

• easy
• nonn

Comments

Also see comments in A046022 = primes together with 1 and 4.

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..150

Crossrefs

Cf. A000142, A000290, A046022, A056653.

Programs

Mathematica

f[n_]:=If[PrimeQ[n]||n == 4,0,n!/n^2];Select[Table[f[n],{n,1,40}],#>0&]  (* Geoffrey Critzer, Oct 26 2012 *)
Select[#!/#^2&/@Range[30],IntegerQ] (* Harvey P. Dale, Jul 17 2024 *)

Formula

a(n) = A000142(m)/A000290(m) where m = A056653(n). - Jason Yuen, Sep 20 2024

Extensions

More terms from Alois P. Heinz, Oct 26 2012