id:A120445 - OEIS Search Results

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A120445

Number of different convex inscribed polygons with n pair of sides of lengths d1, d2, ..., dn; di =/= dj if i=/=j. Or number of necklaces with n pairs of beads, each pair of one among n colors.

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1, 2, 11, 171, 5736, 312240, 24327000, 2554072920, 347351195520, 59397023589120, 12473374574505600, 3155763762320400000, 946729128624509260800, 332301924146113021900800, 134914581203304233287756800 (list; graph; listen)

	OFFSET	`1,2`
	LINKS	`n-digonos.`
	FORMULA	`a(n) = ((2n)!/2^n + (n+1)n! + nn!)/(4n)`
	EXAMPLE	`a(2) = 2 because there are two quadrilaterals with sides {1, 1, 2, 2}: a comet and a rectangle.`
	CROSSREFS	`Sequence in context: A067968 A013050 A051255 this_sequence A003088 A121231 A122527` `Adjacent sequences: A120442 A120443 A120444 this_sequence A120446 A120447 A120448`
	KEYWORD	`nonn`
	AUTHOR	`Ignacio Larrosa Canestro (ilarrosa(AT)mundo-r.com), Jul 19 2006`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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