[math-fun] Colouring the queen graphs

I earlier wrote

I thought it lacked a lot of good material, so I wrote a column about some of that missing material.

http://www.maa.org/editorial/mathgames/mathgames_04_11_05.html

Have 454 solutions of the 12 sets of 12 queens on a 12×12 board been seen anywhere before? (If Guenter Stertenbrink and Patrick Hamlyn aren't yet on the Math-fun list, perhaps they should be.)

Guenter was quick to write to me. He pointed me at http://www.cs.concordia.ca/~chvatal/queengraphs.html The queen graph has been proven impossible for 2, 3, 4, 6, 8, 9, 10. Solutions have been found for all other cases up to 25. The state of the order-26 queen graph is unresolved. It is hypothesized that the queen graph is solvable for all n>10. Ed Pegg Jr