A128656 - OEIS

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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; text; internal format)

	OFFSET	`1,1`
	LINKS	`Table of n, a(n) for n=1..22.` `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 * A208044 A291697 A047851` `Adjacent sequences: A128653 A128654 A128655 * A128657 A128658 A128659`
	KEYWORD	`nonn`
	AUTHOR	`Ralf Stephan, May 08 2007`
	STATUS	`approved`

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Last modified March 25 23:47 EDT 2023. Contains 361529 sequences. (Running on oeis4.)