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A060963 Number of pairings of the first 2n positive integers so that the absolute differences of each pair are different. 9
1, 1, 1, 5, 29, 145, 957, 8397, 85169, 944221, 11639417, 160699437, 2430145085, 39776366397, 703161838717, 13369111112753 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Number of perfect Skolem-type sequences.

LINKS

Table of n, a(n) for n=0..15.

G. Nordh, Perfect Skolem sequences, arXiv:math/0506155 [math.CO], 2005.

EXAMPLE

a(3)=5 since the 5 pairings of {1, 2, 3, 4, 5, 6} are {1, 3} {2, 6} {4, 5}, {1, 5} {2, 3} {4, 6}, {1, 5} {2, 4} {3, 6}, {1, 4} {2, 6} {3, 5}, {1, 6} {2, 5} {3, 4}.

CROSSREFS

Cf. A261516, A261517.

Sequence in context: A163082 A189430 A273078 * A107002 A027864 A272839

Adjacent sequences:  A060960 A060961 A060962 * A060964 A060965 A060966

KEYWORD

nonn

AUTHOR

Erich Friedman, May 08 2001

EXTENSIONS

Offset corrected by Alois P. Heinz, Sep 14 2015

a(14) from Fausto A. C. Cariboni, Mar 03 2017

a(15) from Fausto A. C. Cariboni, Apr 10 2017

STATUS

approved

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Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)