A320333 a(n) is the number of pairings of the first 2*k positive integers into k pairs (xi, yi) such that the k numbers (xi + yi) mod k are all different where k = 2*n + 1.

1, 9, 145, 4641, 231417, 16770369, 1671395713

Offset

0,2

Comments

It can be seen as interesting that a(t) = A178185(t+1) for 0 <= t <= 3.

Links

Table of n, a(n) for n=0..6.

Example

a(1) = 9 because {(1,4), (2,5), (3,6)}, {(1,5), (2,6), (3,4)}, {(1,6), (2,4), (3,5)}, {(1,3), (2,6), (4,5)}, {(1,5), (2,3), (4,6)}, {(1,6), (2,3), (4,5)}, {(1,3), (2,4), (5,6)}, {(1,2), (3,5), (4,6)}, {(1,2), (3,4), (5,6)} are corresponding sets.

Crossrefs

Cf. A060963, A178185, A320129.

Sequence in context: A064091 A132060 A362656 * A178185 A244822 A299319

Adjacent sequences: A320330 A320331 A320332 * A320334 A320335 A320336

Keyword

nonn,more

Author

Altug Alkan, Oct 11 2018

Status

approved