Do you mean the smallest whole number that hasn't appeared yet? But yup, that's a well-known recursion for XOR, important in combinatorial game theory, in whic

Do you mean the smallest whole number that hasn't appeared yet? But yup, that's a well-known recursion for XOR, important in combinatorial game theory, in which context it's often known as the Nim sum. (Note by the way, that the initial condition about (0,0) can be omitted -- at that point, there are no numbers in that row or column, so the smallest one available is 0!) Topics you might want to look up: https://en.wikipedia.org/wiki/Combinatorial_game_theory https://en.wikipedia.org/wiki/Combinatorial_game_theory https://en.wikipedia.org/wiki/Nim https://en.wikipedia.org/wiki/Nim https://en.wikipedia.org/wiki/Sprague%E2%80%93Grundy_theorem https://en.wikipedia.org/wiki/Sprague%E2%80%93Grundy_theorem https://en.wikipedia.org/wiki/Mex_(mathematics) https://en.wikipedia.org/wiki/Mex_(mathematics) https://en.wikipedia.org/wiki/Nimber https://en.wikipedia.org/wiki/Nimber