OFFSET

0,3

COMMENTS

a(n) is also the number of ways to place n nonattacking pieces rook + leaper[2,3] on an n X n chessboard (in fairy chess the leaper [2,3] is called a zebra).

LINKS

V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)

FORMULA

Asymptotic: a(n)/n! ~ 1/e^4.

CROSSREFS

KEYWORD

nonn,more,hard

AUTHOR

Vaclav Kotesovec, Apr 23 2011

STATUS

approved