A218385 - OEIS

%I #8 Oct 30 2012 16:51:04

%S 4,90,560,4032,302400,34214400,415134720,5448643200,1162377216000,

%T 320118685286400,5792623828992000,110586454917120000,

%U 46833363657400320000,1034080669555399065600,23863400066663055360000,574489260864110592000000,14403266468807344128000000,10162944820390462016716800000

%N (n-2)!/n when an integer.

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

%e a(1) = 4 because 4!/6 = 4. That is, 6 divides 4!.

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

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

%Y Cf. A129906.

%K nonn

%O 1,1

%A _Geoffrey Critzer_, Oct 27 2012