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%I #13 Oct 26 2019 14:30:59
%S 1,1,6,100,3375,194481,17210368,2176782336,373669453125,
%T 83733937890625,23762680013799936,8335775831236199424,
%U 3543686674874777831491,1795856326022129150390625,1069932053790720000000000000
%N a(n) = C(n, 2)^(n-3) = (n(n-1)/2)^(n-3).
%C 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
%H Saverio Caminiti and Emanuele G. Fusco, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL10/Caminiti/caminiti.html">On the Number of Labeled k-arch Graphs</a>, Journal of Integer Sequences, Vol 10 (2007), Article 07.7.5.
%H C. Lamathe, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL7/Lamathe/lamathe2.html">The number of labeled k-arch graphs</a>, Journal of Integer Sequences, Vol. 7 (2004), Article 04.3.1.
%H B. Leclerc, <a href="https://doi.org/10.4000/msh.2858">Graphes d'arches</a>, Math. Sci. Hum. 157 (2002), 27-48.
%p seq( (n*(n-1)/2)^(n-3), n=2..19 );
%t Table[Binomial[n,2]^(n-3),{n,2,20}] (* _Harvey P. Dale_, Jan 25 2012 *)
%Y Cf. A098722, A098723, A098724
%K easy,nonn
%O 2,3
%A Cedric Lamathe (lamathe(AT)loria.fr), Sep 30 2004