A206477 (Number of permutations of {1,2,...,n} for which sums of three consecutive numbers (with wraparound) are all distinct)/2n.

3, 3, 36, 76, 690, 2996, 22368, 147472, 1284653, 11006509

Offset: 4

Author

Steve Butler, Feb 08 2012

Keywords

• hard
• nonn

Comments

Essentially different ways 1,2,...,n can be placed around a circle so that sums of three consecutive numbers are distinct.

Examples

			a(4)=3 because up to rotation/reflection the only three permutations which work are 1234, 1243, and 1324
		

Crossrefs

Cf. A040018