A128656 - OEIS

This site is supported by donations to The OEIS Foundation.

A128656

Number of polygons on n vertices with four faces such that the source of the polygon lies on exactly two faces.

2, 8, 44, 240, 1248, 6224, 30052, 141536, 653744, 2973072, 13351192, 59333408, 261378944, 1142885664, 4965331028, 21452209600, 92230169232, 394819386896, 1683663903016, 7155148746912, 30313584232640, 128067598573408 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	LINKS	`T. Mansour and S. Severini, Grid polygons from permutations and their enumeration by the kernel method`
	FORMULA	`a(n) = 2(n+2) * 4^(n-3) - 2(n+1) C(2*n-4,n-3).`
	CROSSREFS	`Sequence in context: A018985 A018986 A192469 * A047851 A177260 A121747` `Adjacent sequences: A128653 A128654 A128655 * A128657 A128658 A128659`
	KEYWORD	`nonn`
	AUTHOR	`Ralf Stephan, May 08 2007`

Content is available under The OEIS End-User License Agreement .

Last modified February 16 04:47 EST 2012. Contains 205860 sequences.