A218385 (n-2)!/n when an integer.

4, 90, 560, 4032, 302400, 34214400, 415134720, 5448643200, 1162377216000, 320118685286400, 5792623828992000, 110586454917120000, 46833363657400320000, 1034080669555399065600, 23863400066663055360000, 574489260864110592000000, 14403266468807344128000000, 10162944820390462016716800000

Offset

1,1

Comments

n divides (n-2)! for all composite n >= 6.

Links

Table of n, a(n) for n=1..18.

Example

a(1) = 4 because 4!/6 = 4. That is, 6 divides 4!.
a(2) =90 because the next composite number after 6 is 8. 6!/8 = 90, which means 8 divides 6!

Mathematica

f[n_] := If[PrimeQ[n], 0, (n-2)!/n]; Select[Table[f[n], {n, 30}], IntegerQ[#] && #>0&]

Crossrefs

Cf. A129906.

Sequence in context: A205295 A292304 A337081 * A189882 A067767 A240379

Adjacent sequences: A218382 A218383 A218384 * A218386 A218387 A218388

Keyword

nonn

Author

Geoffrey Critzer, Oct 27 2012

Status

approved