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

1,4

Comments

An empress moves like a rook and a knight.

Links

Table of n, a(n) for n=1..16.

V. Kotesovec, Non-attacking chess pieces

Example

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

Crossrefs

Cf. A137774, A002562.

Sequence in context: A261582 A135686 A378416 * A151961 A025229 A073951

Adjacent sequences: A218241 A218242 A218243 * A218245 A218246 A218247

Keyword

nonn,more

Author

Witold Dlugosz, Oct 24 2012

Status

approved