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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. 2
1, 1, 2, 2, 7, 12, 22, 26, 85, 226, 717, 1695, 5071, 14275, 47405, 176747, 638329, 2166516 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

Table of n, a(n) for n=0..17.

David A. Corneth, Illustration for a(4)

EXAMPLE

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.

CROSSREFS

Cf. A002968, A060963, A272363, A320129.

Sequence in context: A005298 A063692 A292615 * A123209 A123604 A321306

Adjacent sequences:  A320165 A320166 A320167 * A320169 A320170 A320171

KEYWORD

nonn,more

AUTHOR

Altug Alkan, Oct 07 2018

EXTENSIONS

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

STATUS

approved

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Last modified October 23 08:40 EDT 2021. Contains 348211 sequences. (Running on oeis4.)