A137334 Number of n X n crossword puzzles with dihedral symmetry group, for n odd. 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.

1, 2, 10, 45, 302, 3102, 45795

Offset

3,2

Comments

The number of such puzzles for an even n = 2m is equal to the number of (2m-1) X (2m-1) puzzles.

Links

Table of n, a(n) for n=3..9.

Marc Brodie, Mathematica program

Example

a(5) = 2 because, using 0's for white squares and 1's for black squares, the only two 5 X 5 puzzles with dihedral symmetry group are:
00000
00000
00000
00000
00000
and
10001
00000
00000
00000
10001

Crossrefs

Cf. A130578, A133226, A133253, A133258.

Sequence in context: A192704 A005963 A140588 * A209010 A306752 A306859

Adjacent sequences: A137331 A137332 A137333 * A137335 A137336 A137337

Keyword

nonn

Author

Marc Brodie (mbrodie(AT)wju.edu), Apr 07 2008

Status

approved