A129906 - OEIS

A129906

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

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

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OFFSET

1,2

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

FORMULA

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

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 *)

CROSSREFS

Cf. A000142, A000290, A046022, A056653.

Sequence in context: A015268 A202577 A059420 * A125722 A336412 A226731

Adjacent sequences: A129903 A129904 A129905 * A129907 A129908 A129909

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Jun 09 2007

EXTENSIONS

More terms from Alois P. Heinz, Oct 26 2012

STATUS

approved