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

1,2

Links

Table of n, a(n) for n=1..13.

Sean A. Irvine, Java program (github)

Kevin Ryde, C Code

Example

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.

Prog

(Java) /* See links. */
(C) /* See links. */

Crossrefs

Cf. A048200, A378834 (LRE ways).

Sequence in context: A246576 A358273 A215894 * A287641 A265312 A241531

Adjacent sequences: A061542 A061543 A061544 * A061546 A061547 A061548

Keyword

more,nonn

Author

Naohiro Nomoto, May 16 2001

Extensions

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

a(13) from Kevin Ryde, Dec 28 2024

Status

approved