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A081484

Consider the mapping f(a/b) = (a^2 + b)/(a^2 - b). Taking a =2, b = 1 to start with and carrying out this mapping repeatedly on each new (reduced) rational number gives the following sequence 2/1,5/3,14/11,207/185,... Sequence contains the denominators.

The mapping f(a/b) = (a + b)/(a - b). Taking a = 2 b = 1 to start with and carrying out this mapping repeatedly on each new (reduced)rational number gives the periodic sequence 2/1,3/1,2/1,3/1,...