A078603 Number of ways of arranging the numbers 1..n in a circle so that adjacent numbers do not differ by 1 mod n.

1, 0, 0, 0, 2, 6, 46, 354, 3106, 29926, 315862, 3628906, 45132474, 604534846, 8680957902, 133082437730, 2169964347282, 37505486702678, 685046187718022, 13186335387855770, 266816610979894058, 5662225862272325550

Offset: 1

Author

N. J. A. Sloane, Dec 11 2002

Keywords

• nonn

Examples

			a(5) = 2: 1 3 5 2 4, 1 4 2 5 3; a(6) = 6: 1 4 6 2 5 3, 1 5 2 4 6 3, 1 5 3 6 2 4, 1 3 6 4 2 5, 1 4 2 6 3 5, 1 3 5 2 6 4.
		

Links

• Index entries for sequences related to shoe lacings

Crossrefs

Twice A002816.

The sequence n*a(n) is A089222.

See also A078628.

Formula

For n>1, a(n) = 2*A002816(n).

Extensions

The sequence was missing a zero; also added a cross-reference Joel B. Lewis, Jan 28 2010