A206478 - OEIS

A206478

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

12, 8, 76, 694, 2529, 23679, 177885, 1482021, 14666021

(list; graph; refs; listen; history; text; internal format)

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

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

KEYWORD

hard,nonn

AUTHOR

Steve Butler, Feb 08 2012

STATUS

approved