Computable numbers are the real numbers that can be computed to within any desired precision by a finite, terminating algorithm.
A function f \colon \mathbb{R} \to \mathbb{R} is sequentially computable if, for every computable sequence \{x_i\}_{i=1}^\infty of real numbers, the sequence \{f(x_i) \}_{i=1}^\infty is also computable.