id:A038718 - OEIS Search Results

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Number of permutations P of {1,2,...,n} such that P(1)=1 and |P^-1(i+1)-P^-1(i)| equals 1 or 2 for i=1,2,...,n-1.

+0
2

1, 1, 2, 4, 6, 9, 14, 21, 31, 46, 68, 100, 147, 216, 317, 465, 682, 1000, 1466, 2149, 3150, 4617, 6767, 9918, 14536, 21304, 31223, 45760, 67065, 98289, 144050, 211116, 309406, 453457, 664574, 973981, 1427439, 2092014, 3065996, 4493436, 6585451 (list; graph; listen)

	OFFSET	`1,3`
	FORMULA	`G.f.: (x^2-x+1)/(x^4-x^3+x^2-2x+1). a(n) = a(n-1) + a(n-3) + 1. - Joseph Myers (jsm(AT)polyomino.org.uk), Feb 03 2004`
	CROSSREFS	`Cf. A003274.` `Cf. A003410.` `Adjacent sequences: A038715 A038716 A038717 this_sequence A038719 A038720 A038721` `Sequence in context: A139135 A097197 A119737 this_sequence A042942 A005687 A024849`
	KEYWORD	`nonn`
	AUTHOR	`John W. Layman (layman(AT)math.vt.edu), May 02 2000`
	EXTENSIONS	`More terms from Joseph Myers (jsm(AT)polyomino.org.uk), Feb 03 2004`

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Last modified October 15 20:12 EDT 2008. Contains 145099 sequences.

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