A278686 Number of non-equivalent ways to place 7 non-attacking ferses on an n X n board.

0, 0, 0, 27, 4860, 164423, 2651890, 25981150, 180378380, 971905679, 4316504623, 16457726539, 55463445891, 168782705327, 471407278652, 1223710587908, 2982045310010

Offset

1,4

Comments

A fers is a leaper [1, 1].

Rotations and reflections of placements are not counted. If they are to be counted, see A201248.

Links

Table of n, a(n) for n=1..17.

Wikipedia, Fairy chess piece

Example

There are 27 non-equivalent ways to place 7 non-attacking ferses (X) on a 4 X 4 board, rotations and reflections being ignored, e.g., these two:
   XXXX   X.XX
   ....   ....
   XXX.   X.X.
   ....   X.X.

Crossrefs

Cf. A201248, A232567 (2 ferses), A278682 (3 ferses), A278683 (4 ferses), A278684 (5 ferses), A278685 (6 ferses), A278687, A278688.

Sequence in context: A223327 A211927 A298595 * A046367 A059795 A211928

Adjacent sequences: A278683 A278684 A278685 * A278687 A278688 A278689

Keyword

nonn,more

Author

Heinrich Ludwig, Dec 02 2016

Status

approved