A143891 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric about the diagonal and under 90-degree rotation.

1, 2, 1, 5, 2, 15, 7, 68, 23, 370, 104, 2649, 571, 25209, 4176, 313503, 39827, 5212881, 500254, 114569731, 8348616

Offset

0,2

Links

Table of n, a(n) for n=0..20.

Crossrefs

Sequence in context: A109738 A258307 A343254 * A030400 A115345 A194092

Adjacent sequences: A143888 A143889 A143890 * A143892 A143893 A143894

Keyword

nonn,more,hard

Author

R. H. Hardin, Sep 04 2008

Status

approved