A218101 The number of simple labeled graphs on n nodes that have exactly n(n-1)/4 edges.

1, 0, 0, 20, 252, 0, 0, 40116600, 9075135300, 0, 0, 7219428434016265740, 27217014869199032015600, 0, 0, 96614908840363322603893139521372656, 5949105755928259715106809205795376486500, 0, 0, 90717484605833107953850163563674201296374152790550788800, 90492479540310008180848641429024900729436748166512078795479440, 0, 0

Offset

1,4

Links

Table of n, a(n) for n=1..23.

Mathematica

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}]

Crossrefs

Sequence in context: A055757 A022744 A081143 * A241228 A306290 A075469

Adjacent sequences: A218098 A218099 A218100 * A218102 A218103 A218104

Keyword

nonn

Author

Geoffrey Critzer, Oct 20 2012

Status

approved