by **vinays84** » Mon Apr 17, 2006 6:45 am

Thanks keith. They give a number there, but I believe this is the number of unique grids, not unique grid structures. I suppose you can find the number of unique grids by simply dividing this number by 9!. This yields 72^2 × 2^7 × 27,704,267,971, which they say was derived through logic and brute force computation. However, the exact logical methods are not stated. If anyone has a basic idea to how these numbers were found please let me know, because..well..I'm curious.

-Vinay