I have found various Internet sources claiming words to the following effect, regarding the board-game Go: "It is commonly said that no game has ever been played twice. This may be true: On a 19×19 board, there are about 3^361×0.012 = 2.1×10^170 possible positions, most of which are the end result of about (120!)^2 = 4.5×10^397 different (no-capture) games, for a total of about 9.3×10^567 games. Allowing captures gives as many as 10^(7.49×10^48) possible games, most of which last for over 1.6×10^49 moves! (By contrast, the number of legal positions in chess is estimated to be between 10^43 and 10^50, and physicists estimate that there are not more than 10^90 protons in the entire universe.)" I would love to hear where certain of these figures come from, or perhaps to understand how to calculate the game-tree complexity of Go in the first place. Where (120!)^2 and 9.3×10^567 are coming from seems unclear, let alone 10^(7.49×10^48). I would have thought that, disallowing captures, (19*19)! gives an estimate, but I appear to have severely overcounted as (19*19)! = 1.44*10^768. Any idea how to reach a better estimate? Including with captures?