A285485 Number of (n+1)-extended Skolem sequences of order n.

0, 0, 2, 2, 0, 0, 44, 260, 0, 0, 33104, 203712, 0, 0, 75499696, 621309008, 0, 0, 492805156768, 5068810602400, 0, 0, 7346944632542720

Offset: 1

Author

Fausto A. C. Cariboni, Apr 19 2017

Keywords

• nonn
• more

Comments

Number of Rosa sequences of order n.

a(n) computed counting reflected solutions.

Examples

			For n = 3, there are 2 solutions: 1 1 3 0 2 3 2 and 2 3 2 0 3 1 1.
For n = 4, there are 2 solutions: 1 1 3 4 0 3 2 4 2 and 2 4 2 3 0 4 3 1 1.
		

Links

• N. Francetić, E. Mendelsohn, A survey of Skolem-type sequences and Rosa's use of them, Math. Slovaca 59 (2009), pp. 39-76
• Jeppe Winther Larsen, Counting the Skolem sequences using inclusion-exclusion
• R. Rees, N. Shalaby, A. Sharary, Indecomposable Skolem and Rosa sequences

Crossrefs

Cf. A004077, A004075

Extensions

a(1)-a(18) from Jeppe Winther Larsen (jwl(AT)itu.dk), Oct 12 2009

a(1)-a(18) confirmed, a(19)-a(22) from Fausto A. C. Cariboni, Apr 19 2017

a(23) from Fausto A. C. Cariboni, May 11 2017