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

Offset

1,2

Comments

Sequence suggested by Leroy Quet on the SeqFan mailing list.

Links

Table of n, a(n) for n=1..15.

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: A101713 A240761 A342317 * A244060 A333185 A236106

Adjacent sequences: A117538 A117539 A117540 * A117542 A117543 A117544

Keyword

nonn

Author

Giovanni Resta, Mar 28 2006

Status

approved