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a(n) = A000166(n)*binomial(n,2).
0

%I #9 Sep 09 2017 23:23:24

%S 0,0,1,6,54,440,3975,38934,415324,4805856,60073245,807651350,

%T 11630179506,178681848696,2918470195459,50511984152070,

%U 923647710209400,17795612550034304,360361154138194809,7652375096699313126,170052779926651402990,3947014523560698353400

%N a(n) = A000166(n)*binomial(n,2).

%p with (combstruct):with (combinat):a:=proc(m) [ZL, {ZL=Set(Cycle(Z, card>=m))}, labeled]; end: ZLL:=a(2):seq(count(ZLL, size=n)*binomial(n,2), n=0..21); # _Zerinvary Lajos_, Jun 11 2008

%t Table[Subfactorial[n]*Binomial[n, 2], {n, 0, 22}] (* _Zerinvary Lajos_, Jul 09 2009 *)

%Y Cf. A000387.

%K nonn

%O 0,4

%A _N. J. A. Sloane_, Nov 10 2001