A117542 Number of permutations P of 1..n such that in P and in the inverse of P, every pair of adjacent numbers and the first and last number, are relatively prime.

1, 2, 6, 8, 36, 16, 127, 320, 581, 1564, 13565, 13760, 149186, 773727, 540538

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)=8, since the 8 permutations (1,2,3,4), (1,4,3,2), (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, A117541.

Sequence in context: A019199 A094678 A076507 * A045653 A235320 A152158

Adjacent sequences: A117539 A117540 A117541 * A117543 A117544 A117545

Keyword

nonn

Author

Giovanni Resta, Mar 28 2006

Status

approved