1,2

a(5) = 1 since "xrrxrrxrxr" is the shortest only sequence reversing "ABCDE".

Table of n, a(n) for n=1..8.

For n = 6 there are 2 possibilities: A048200(6) = 15. -> Two minimal XR-sequences with length 15 exist. -> "xrxrrxrxrrxrrrx" "rxrrxrxrrxrxrrx"; so a(6) = 2.

Cf. A048200.

Sequence in context: A117211 A246576 A215894 * A287641 A265312 A241531

Adjacent sequences: A061542 A061543 A061544 * A061546 A061547 A061548

more,nonn

Naohiro Nomoto, May 16 2001

approved