

A225623


Number of ways to arrange 2n queens on an n X n chessboard, with no more than 2 queens in each row, column or diagonal.


2




OFFSET

1,3


COMMENTS

This problem is slightly different from A000769 or A219760. In the first example on an 8 x 8 board, are the queens c7, d5 and e3 (or queens a2, c5 and e8) in a line, but such case is allowed. The elementary step can be only [0,1], [1,0] or [1,1], not for example [1,2] or [2,3].


LINKS

Table of n, a(n) for n=1..9.
Vaclav Kotesovec, Examples


CROSSREFS

Cf. A000170, A000769, A001499, A001501, A058528, A075754, A172544, A172541.
Sequence in context: A222080 A122708 A292424 * A005366 A068392 A164893
Adjacent sequences: A225620 A225621 A225622 * A225624 A225625 A225626


KEYWORD

nonn,more,hard


AUTHOR

Vaclav Kotesovec, Aug 04 2013


EXTENSIONS

Definition clarified by Vaclav Kotesovec, Dec 18 2014


STATUS

approved



