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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. 1
2, 16, 144, 2048, 46400, 1262592, 44493568, 2000420864, 110023308288 (list; graph; refs; listen; history; text; internal format)
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: A003768 A214767 A300412 * A162440 A103885 A262266

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

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Last modified December 12 09:36 EST 2019. Contains 329953 sequences. (Running on oeis4.)