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

Author

Erich Friedman, May 08 2001

Keywords

• nonn
• more

Comments

Number of perfect Skolem-type sequences.

Examples

			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}.
		

Links

• Edward Moody, Java program for calculating entries in this sequence and A322178
• G. Nordh, Perfect Skolem sequences, arXiv:math/0506155 [math.CO], 2005.

Crossrefs

Cf. A261516, A261517, A322178.

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