From Tardis Wiki, the free Doctor Who reference

A mathematician was a person whose primary field of study was mathematics.

Doctor Who was the greatest human mathematician. (PROSE: The Equations of Dr Who) Lady Peinforte hired a mathematician to calculate the path of Nemesis. (TV: Silver Nemesis)

Another mathematician resided within psychspace and was part of the Great Melding Minds. (COMIC: Forever Dreaming)

The Logopolitans were a race of mathematicians on the planet Logopolis. (TV: Logopolis)