From a very strict point of view, however, mathematics is NOT a "science" itself. By "very strict" I mean defining a science as based on the "scientific method":
1. Observe and experiment
2. From the observations, develop as many theories as possible
3. From the theory predict results of additional experiments
4. Do the experiments to eliminate those theories that predicted incorrect results
5. Repeat
(Mathematics is only really used in part (3) of that.)
Mathematics is not a science in that it does not depend upon the results of experiments. More simply put, science depends upon inductive logic while mathematics depends upon deductive logic.
In fact, I would go further. Science, because of its insistence upon correspondence with the result of experimentation, is necessarily based on a "Realistic" philosophy while mathematics, insisting on a logical progression from axioms, is necessarily based on an "Idealistic" philosophy.