A098721 a(n) = C(n, 2)^(n-3) = (n(n-1)/2)^(n-3).

1, 1, 6, 100, 3375, 194481, 17210368, 2176782336, 373669453125, 83733937890625, 23762680013799936, 8335775831236199424, 3543686674874777831491, 1795856326022129150390625, 1069932053790720000000000000

Offset

2,3

Comments

There is a flaw in the paper by Lamathe that we point out in our contribution. This sequence does not give the number of labeled 2-arch graphs (here named arch graphs) on n nodes. The correct sequence is given in our paper. - Saverio Caminiti and Emanuele G. Fusco (fusco(AT)di.uniroma1.it), Sep 18 2007

Links

Table of n, a(n) for n=2..16.

Saverio Caminiti and Emanuele G. Fusco, On the Number of Labeled k-arch Graphs, Journal of Integer Sequences, Vol 10 (2007), Article 07.7.5.

C. Lamathe, The number of labeled k-arch graphs, Journal of Integer Sequences, Vol. 7 (2004), Article 04.3.1.

B. Leclerc, Graphes d'arches, Math. Sci. Hum. 157 (2002), 27-48.

Maple

seq( (n*(n-1)/2)^(n-3), n=2..19 );

Mathematica

Table[Binomial[n, 2]^(n-3), {n, 2, 20}] (* Harvey P. Dale, Jan 25 2012 *)

Crossrefs

Cf. A098722, A098723, A098724

Sequence in context: A278430 A374889 A131311 * A291837 A214381 A078629

Adjacent sequences: A098718 A098719 A098720 * A098722 A098723 A098724

Keyword

easy,nonn

Author

Cedric Lamathe (lamathe(AT)loria.fr), Sep 30 2004

Status

approved