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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
1, 9, 145, 4641, 231417, 16770369, 1671395713 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
It can be seen as interesting that a(t) = A178185(t+1) for 0 <= t <= 3.
LINKS
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
Sequence in context: A064091 A132060 A362656 * A178185 A244822 A299319
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Oct 11 2018
STATUS
approved

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Last modified May 24 07:02 EDT 2024. Contains 372772 sequences. (Running on oeis4.)