A132444 Number of n x n crossword puzzles with rotational symmetry and exactly one black square per row, up to symmetry.

0, 0, 0, 1, 1, 5, 6, 60, 93

Offset: 3

Author

Marc Brodie (mbrodie(AT)wju.edu), Aug 21 2007

Keywords

• nonn

Comments

Acceptable crossword puzzles must have all words of length 3 or more, at least one word in each row and each column and be connected. Since the puzzles counted in sequence A132443 come naturally in pairs (by reflective symmetry), the numbers in this sequence are obtained by dividing the corresponding numbers in A132443 by 2.

Examples

			a(6) = 1 because up to symmetry, the only 6 X 6 crossword puzzle with exactly one black square in each row (using 1's for black squares and 0's for white) is:
100000
100000
100000
000001
000001
000001
		

Crossrefs

Cf. A130578, A132443, A132445, A132446.

Programs

Maple

See the program for A132443