OFFSET
1,2
COMMENTS
(In fairy chess the rider [1,2] is called a Nightrider, Rook + Nightrider = Waran.)
a(n) is also the number of permutations p of 1,2,...,n satisfying |p(i+k) - p(i)| <> 2k AND |p(j+2k) - p(j)| <> k for all i >= 1, j >= 1, k >= 1, i+k <= n, j+2k <= n.
LINKS
V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech).
Wikipedia, Fairy chess piece
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 29 2011
STATUS
approved