A061545 Number of pair-exchange / set-rotate sequences achieving the minimum length of A048200(n).

0, 2, 1, 1, 1, 2, 4, 16, 40, 512, 1472, 65536, 208896

Offset: 1

Author

Naohiro Nomoto, May 16 2001

Keywords

• more
• nonn

Examples

			Let "r" denote rotation and "x" an exchange.
For n = 5, the shortest sequence reversing "ABCDE" has length A048200(5) = 10, the only sequence doing so is "xrrxrrxrxr", so a(5) = 1.
For n = 6, we have A048200(6) = 15, but there are 2 solutions of this length "xrxrrxrxrrxrrrx" and "rxrrxrxrrxrxrrx", so a(6) = 2.
		

Links

• Sean A. Irvine, Java program (github)
• Kevin Ryde, C Code

Crossrefs

Cf. A048200, A378834 (LRE ways).

Programs

C

/* See links. */

Java

/* See links. */

Extensions

Sequence revised and a(9)-a(12) from Sean A. Irvine, Feb 21 2023

a(13) from Kevin Ryde, Dec 28 2024