A218244 Number of inequivalent (rotationally and reflectively distinct) ways to place n nonattacking empresses on n X n board.

1, 1, 1, 3, 6, 21, 75, 415, 2621, 21066, 195485, 2083543, 24744474, 323438322, 4596672672, 70440521310

Offset: 1

Author

Witold Dlugosz, Oct 24 2012

Keywords

• nonn
• more

Comments

An empress moves like a rook and a knight.

Examples

			a(4) = 3: different ways to place 4 nonattacking empresses on a 4 X 4 board:
Xooo Xooo oXoo
oXoo oooX Xooo
ooXo ooXo oooX
oooX oXoo ooXo
		

Links

• V. Kotesovec, Non-attacking chess pieces

Crossrefs

Cf. A137774, A002562.