A170808 Number of permutations of 1..n with all differences of elements separated by distances 1 or 2 being respectively unique.

1, 2, 4, 12, 40, 116, 252, 768, 2704, 12756, 63168, 338308, 1956876, 11971780, 77909884, 535178056, 3906154920, 30146769464, 244980749052, 2094507398508

Offset

1,2

Comments

(Empirical) Equals A008404 for n<=2m+2, where m is the maximum difference separation 2.

Links

Table of n, a(n) for n=1..20.

Crossrefs

Sequence in context: A170811 A170810 A170809 * A366579 A099214 A126946

Adjacent sequences: A170805 A170806 A170807 * A170809 A170810 A170811

Keyword

nonn

Author

R. H. Hardin Dec 02 2009

Status

approved