[math-fun] Number of legal 18x18 Go positions

-- The important thing seems to be the ratio 2.9757341920433572493 rather than the naive estimate 3. Not a huge shrink. Their more precise estimate for mXn grid is L(m,n) =approx= 0.850639925845714538 * 0.96553505933837387^(m+n) * 2.97573419204335724938^(m*n)