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A206478
(Number of permutations of {1,2,...,n} for which sums of four consecutive numbers (with wraparound) are all distinct)/2n
0
12, 8, 76, 694, 2529, 23679, 177885, 1482021, 14666021
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.
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
Sequence in context: A307171 A040134 A258641 * A164675 A121961 A168386
KEYWORD
hard,nonn
AUTHOR
Steve Butler, Feb 08 2012
STATUS
approved