A024915 Number of positions in which 2n semi-queens may be placed on an 2n X 2n toroidal board, with only one semi-queen attacking another semi-queen; also, number of interval method wirings for a cryptographic rotor of size 2n.

2, 16, 144, 2048, 46400, 1262592, 44493568, 2000420864, 110023308288

Offset

1,1

Links

Table of n, a(n) for n=1..9.

Sean A. Irvine, Java program (github)

J. Savard, The Interval Method [Wayback Machine copy]

Example

There are 144 possible interval method wirings for a 6-contact 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).

Crossrefs

Cf. A006717.

Sequence in context: A214767 A300412 A333727 * A162440 A337793 A103885

Adjacent sequences: A024912 A024913 A024914 * A024916 A024917 A024918

Keyword

hard,nonn,nice

Author

John Savard (jsavard(AT)ecn.ab.ca)

Extensions

Entry revised and a(9) from Sean A. Irvine, Jul 28 2019

Status

approved