A128650 - OEIS

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A128650

Number of polygons on n vertices with exactly three faces.

0, 4, 16, 60, 224, 840, 3168, 12012, 45760, 175032, 671840, 2586584, 9984576, 38630800, 149768640, 581690700, 2262890880, 8815845720, 34389986400, 134312002440, 525129633600, 2055166429680, 8050465600320, 31561484455800 (list; graph; refs; listen; history; internal format)

	OFFSET	`2,2`
	LINKS	`Vincenzo Librandi, Table of n, a(n) for n = 2..200` `T. Mansour and S. Severini, Grid polygons from permutations and their enumeration by the kernel method`
	FORMULA	`a(n) = 4(n-2)/(n-1) C(2n-4,n-2).` `For n>2, a(n) = 4A001791(n-2).`
	CROSSREFS	`Sequence in context: A089883 A089932 A120926 * A072335 A081161 A032106` `Adjacent sequences: A128647 A128648 A128649 * A128651 A128652 A128653`
	KEYWORD	`nonn`
	AUTHOR	`Ralf Stephan, May 08 2007`

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Last modified February 14 07:08 EST 2012. Contains 205583 sequences.