A040018 (Number of permutations of {1,2,...,n} for which sums of adjacent numbers are all distinct)/2n.

1, 1, 3, 8, 46, 176, 955, 5446, 36122, 259084, 2043944, 17371318, 159616680, 1566391958

Offset

3,3

Comments

Essentially different ways 1,2,3,...,n can be placed around a circle so that sums of adjacent numbers are distinct.

Links

Table of n, a(n) for n=3..16.

Sean A. Irvine, Java program (github)

Crossrefs

Cf. A091217, A006967.

Sequence in context: A132103 A334316 A180508 * A019016 A063859 A210373

Adjacent sequences: A040015 A040016 A040017 * A040019 A040020 A040021

Keyword

nonn,hard,more

Author

Erich Friedman

Extensions

a(10) from Vladeta Jovovic, Aug 25 2007

a(11)-a(13) from Steve Butler, Feb 08 2012

a(14)-a(16) from Sean A. Irvine, Mar 05 2021

Status

approved