Given an NxN board and a supply of 2x1 dominoes, what is the minimum N such that you can tile the board without it being possible to draw a line parallel to any side of the board that does not slice any domino into two?

Source: This problem was found by John Guilford on the rec.puzzles newsgroup.

© Copyright 1997 Stan Wagon. Reproduced with permission.

2 October 1998