John.Tromp@xxxxxxxxxxxxxxxxx writes >here's a short table > >1x1: 1 legal, 2 illegal, prob 0.333333 >2x2: 57 legal, 24 illegal, prob 0.703704 >3x3: 12675 legal, 7008 illegal, prob 0.643957 >4x4: 24318165 legal, 18728556 illegal, prob 0.564925 >5x5: prob ~ 0.489 >9x9: prob ~ 0.234 >19 : prob ~ 0.012 0x0: 1 legal, 0 illegal, prob 1.000000 Nick -- Nick Wedd nick@xxxxxxxxxxxxxxxxx