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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, 1, 0, 3, 12, 25, 0, 475, 5352, 17157, 0, 896535, 15083680, 68879713, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,4
COMMENTS
A variant of A060963, a(n) <= A060963(n) by definition.
LINKS
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
Sequence in context: A047166 A076506 A206917 * A009776 A331241 A068967
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Oct 11 2018
EXTENSIONS
Terms computed by Rémy Sigrist, Oct 11 2018
STATUS
approved

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Last modified May 25 09:23 EDT 2024. Contains 372786 sequences. (Running on oeis4.)