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 A128650 Number of polygons on n vertices with exactly three faces. 4

%I #14 Dec 05 2018 08:11:28

%S 0,4,16,60,224,840,3168,12012,45760,175032,671840,2586584,9984576,

%T 38630800,149768640,581690700,2262890880,8815845720,34389986400,

%U 134312002440,525129633600,2055166429680,8050465600320,31561484455800

%N Number of polygons on n vertices with exactly three faces.

%H Vincenzo Librandi, <a href="/A128650/b128650.txt">Table of n, a(n) for n = 2..200</a>

%H T. Mansour and S. Severini, <a href="https://arxiv.org/abs/math/0603225">Grid polygons from permutations and their enumeration by the kernel method</a>, arXiv:math/0603225 [math.CO], 2006.

%F a(n) = 4*(n-2)/(n-1) * C(2*n-4,n-2).

%F For n>2, a(n) = 4*A001791(n-2).

%t Table[4 Binomial[2n-4, n-3], {n, 2, 25}] (* _Jean-François Alcover_, Dec 05 2018 *)

%K nonn

%O 2,2

%A _Ralf Stephan_, May 08 2007

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Last modified April 17 08:54 EDT 2024. Contains 371763 sequences. (Running on oeis4.)