A004076 Number of hooked Skolem sequences of order n.

0, 1, 2, 0, 0, 38, 124, 0, 0, 12808, 72648, 0, 0, 21878816, 168870048, 0, 0, 113071735648, 1105816948032, 0, 0, 1395701792232832

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• more

Examples

			For n = 3, there are 2 solutions: 1 1 2 3 2 0 3 and 3 1 1 3 2 0 2.
		

References

• CRC Handbook of Combinatorial Designs, 1996, p. 460.

Links

• Jeppe Winther Larsen, Counting the Skolem sequences using inclusion-exclusion, 2009

Extensions

a(15)-a(18) from Jeppe Winther Larsen (jwl(AT)itu.dk), Oct 12 2009

a(4)-a(18) confirmed, a(3) corrected by Fausto A. C. Cariboni, Apr 11 2017

a(19)-a(22) from Fausto A. C. Cariboni, Apr 25 2017