A206478 - OEIS

A206478

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

%I #7 Jan 03 2014 15:59:29

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

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

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

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

%Y Cf. A040018

%K hard,nonn

%O 5,1

%A _Steve Butler_, Feb 08 2012