A320168 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 mod xi) are all different.

1, 1, 2, 2, 7, 12, 22, 26, 85, 226, 717, 1695, 5071, 14275, 47405, 176747, 638329, 2166516

Offset: 0

Author

Altug Alkan, Oct 07 2018

Keywords

• nonn
• more

Comments

How does a(n+1)/a(n) behave as n increases?

Examples

			a(3) = 2 because {(1,3), (2,5), (4,6)} and {(1,5), (2,3), (4,6)} are corresponding sets.
a(4) = 7 because {(1,6), (2,5), (3,8), (4,7)}, {(1,3), (2,7), (4,6), (5,8)}, {(1,7), (2,3), (4,6), (5,8)}, {(1,3), (2,5), (4,7), (6,8)}, {(1,5), (2,3), (4,7), (6,8)}, {(1,2), (3,7), (4,6), (5,8)}, {(1,2), (3,8), (4,7), (5,6)} are corresponding sets.
		

Links

• David A. Corneth, Illustration for a(4)

Crossrefs

Cf. A002968, A060963, A272363, A320129.

Extensions

a(13)-a(17) from Rémy Sigrist, Oct 07 2018