A320334 Number of ways to group the first 2*n positive integers into n pairs (xi, yi) with xi < yi, and such that the n numbers (yi - xi) mod n are all different.

1, 1, 0, 3, 12, 25, 0, 475, 5352, 17157, 0, 896535, 15083680, 68879713, 0

Offset

0,4

Comments

A variant of A060963, a(n) <= A060963(n) by definition.

Links

Table of n, a(n) for n=0..14.

Rémy Sigrist, C++ program for A320334

Example

a(3) = 3 because {(1,4), (2,6), (3,5)}, {(1,5), (2,4), (3,6)}, {(1,6), (2,5), (3,4)} are corresponding sets.

Prog

(C++) See Links section.

Crossrefs

Cf. A060963, A320168, A320333.

Sequence in context: A047166 A076506 A206917 * A009776 A331241 A068967

Adjacent sequences: A320331 A320332 A320333 * A320335 A320336 A320337

Keyword

nonn,more

Author

Altug Alkan, Oct 11 2018

Extensions

Terms computed by Rémy Sigrist, Oct 11 2018

Status

approved