Mathematics was the study of numbers.
Romulus and Remus Sylvest were mathematical geniuses. (TV: The Twin Dilemma) Peter Hutchings was a professor of mathematics at the University of Cambridge. (PROSE: Timewyrm: Revelation)
Some of the companions of the Doctor studied or taught mathematics. Jackson Lake was a mathematics teacher. (TV: The Next Doctor) Alistair Gordon Lethbridge-Stewart taught mathematics at Brendon Public School. (TV: Mawdryn Undead) Adric was awarded a gold star badge for mathematical excellence. (TV: Full Circle) Zoe Heriot introduced herself to the Second Doctor and Jamie McCrimmon as "astrophysicist, pure mathematics major", to which her colleague, Dr Gemma Corwyn, added "with honours." (TV: The Wheel in Space)
Types of mathematics
Block transfer computation
An application of mathematics known as Block Transfer Computation could be used to create objects and alter spacetime. (TV: Logopolis)
The Tenth Doctor mentioned Recreational Mathematics, which involved the study of happy prime numbers. He seemed surprised it wasn't a regularly studied course. (TV: 42)