A060963 Number of pairings of the first 2n positive integers so that the absolute differences of each pair are different.

1, 1, 1, 5, 29, 145, 957, 8397, 85169, 944221, 11639417, 160699437, 2430145085, 39776366397, 703161838717, 13369111112753, 271734091323897

Offset

0,4

Comments

Number of perfect Skolem-type sequences.

Links

Table of n, a(n) for n=0..16.

Edward Moody, Java program for calculating entries in this sequence and A322178

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, A322178.

Sequence in context: A163082 A189430 A273078 * A107002 A339957 A027864

Adjacent sequences: A060960 A060961 A060962 * A060964 A060965 A060966

Keyword

nonn,more

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

a(16) from Edward Moody, Feb 17 2020

Status

approved