A218101 - OEIS

%I #5 Oct 21 2012 02:53:50

%S 1,0,0,20,252,0,0,40116600,9075135300,0,0,7219428434016265740,

%T 27217014869199032015600,0,0,96614908840363322603893139521372656,

%U 5949105755928259715106809205795376486500,0,0,90717484605833107953850163563674201296374152790550788800,90492479540310008180848641429024900729436748166512078795479440,0,0

%N The number of simple labeled graphs on n nodes that have exactly n(n-1)/4 edges.

%t f[n_]:=If[Mod[n,4]==1||Mod[n,4]==0,Binomial[n (n-1)/2,n (n-1)/4],0];Table[f[n],{n,1,25}]

%K nonn

%O 1,4

%A _Geoffrey Critzer_, Oct 20 2012