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A218244
Number of inequivalent (rotationally and reflectively distinct) ways to place n nonattacking empresses on n X n board.
2
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.
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
Sequence in context: A294527 A261582 A135686 * A151961 A025229 A073951
KEYWORD
nonn,more
AUTHOR
Witold Dlugosz, Oct 24 2012
STATUS
approved