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

Author

Altug Alkan, Oct 11 2018

Keywords

• nonn
• more

Comments

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

Examples

			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.