A004077 Number of extended Skolem sequences of order n.

1, 2, 2, 6, 22, 48, 160, 636, 3556, 19488, 95872, 594320, 4459888, 32131648, 227072544, 1875064880, 17851780784, 165367171136, 1506506453568, 15540217445728, 179708231523680, 2034547787823488, 22716589497430656

Offset

0,2

References

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

Links

Table of n, a(n) for n=0..22.

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

Example

From Ruud H.G. van Tol, Mar 15 2026: (Start)
Order 0: 0;
Order 1: 011, 110;
Order 2: 11202, 20211;
Order 3: 1123203, 1130232, 2023113, and their reflections. (End)

Crossrefs

Sequence in context: A320932 A268562 A225942 * A271217 A202743 A007985

Adjacent sequences: A004074 A004075 A004076 * A004078 A004079 A004080

Keyword

nonn,more

Author

N. J. A. Sloane

Extensions

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

a(19)-a(21) from Fausto A. C. Cariboni, Apr 19 2017

a(22) from Fausto A. C. Cariboni, May 07 2017

a(0) from Ruud H.G. van Tol, Mar 15 2026

Status

approved