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

Author

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

Keywords

• hard
• nonn
• nice

Examples

			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).
		

Links

• Sean A. Irvine, Java program (github)
• J. Savard, The Interval Method [Wayback Machine copy]

Crossrefs

Cf. A006717.

Extensions

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