

A206478


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


0




OFFSET

5,1


COMMENTS

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


LINKS

Table of n, a(n) for n=5..13.


EXAMPLE

a(6)=8 because up to rotation/reflection the only three permutations which work are 123465, 123546, 124653, 125364, 126543, 132456, 132645, 136524.


CROSSREFS

Cf. A040018
Sequence in context: A307171 A040134 A258641 * A164675 A121961 A168386
Adjacent sequences: A206475 A206476 A206477 * A206479 A206480 A206481


KEYWORD

hard,nonn


AUTHOR

Steve Butler, Feb 08 2012


STATUS

approved



