Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.
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: A026148 A117211 A215894 * A241531 A221131 A126886
Adjacent sequences: A061542 A061543 A061544 * A061546 A061547 A061548
more,nonn
Naohiro Nomoto, May 16 2001
approved