A117541 - OEIS

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A117541

Number of permutations P of 1..n such that in P and in the inverse of P, every pair of adjacent numbers are relatively prime.

1, 2, 6, 9, 56, 23, 399, 442, 2220, 2386, 71577, 22001, 1179483, 1156519, 4975079 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Sequence suggested by Leroy Quet on the SeqFan mailing list.`
	EXAMPLE	`a(4)=9, since the 9 permutations (1,2,3,4), (1,4,3,2), (2,1,3,4), (2,1,4,3), (2,3,4,1), (4,1,2,3), (3,2,1,4), (3,4,1,2), (4,3,2,1) satisfy the property.`
	CROSSREFS	`Cf. A076220, A117542.` `Sequence in context: A082459 A129831 A101713 * A095105 A052194 A073662` `Adjacent sequences: A117538 A117539 A117540 * A117542 A117543 A117544`
	KEYWORD	`nonn`
	AUTHOR	`Giovanni Resta (g.resta(AT)iit.cnr.it), Mar 28 2006`

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Last modified February 16 17:11 EST 2012. Contains 205938 sequences.