%I
%S 2,16,144,2048,46400,1262592,44493568,2000420864,110023308288
%N Number of positions in which 2n semiqueens may be placed on an 2n X 2n toroidal board, with only one semiqueen attacking another semiqueen; also, number of interval method wirings for a cryptographic rotor of size 2n.
%H Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a024/A024915.java">Java program</a> (github)
%H J. Savard, <a href="http://friedo.szm.com/krypto/JS/home.ecn.ab.ca/~jsavard/crypto.htm">The Interval Method</a> [<a href="http://web.archive.org/web/20041212165407/http://home.ecn.ab.ca/~jsavard/crypto/ro020302.htm">Wayback Machine copy</a>]
%e There are 144 possible interval method wirings for a 6contact rotor, based on 36 rotations of both the whole rotor or one side of the rotor, starting from the four sequences: (1,2,4,6,3,5), (1,2,5,6,3,4), (1,4,3,2,6,5) and (1,6,3,5,4,2), having respectively the patterns of intervals (0,0,1,2,4,5), (0,0,2,5,1,4), (0,2,0,4,1,5) and (0,4,0,1,5,2)
%Y Cf. A006717.
%K hard,nonn,nice
%O 1,1
%A John Savard (jsavard(AT)ecn.ab.ca)
%E Entry revised and a(9) from _Sean A. Irvine_, Jul 28 2019
