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) Danny Pink taught mathematics at Coal Hill School. (TV: Into the Dalek) Spending time in 1138 Essex, the Twelfth Doctor mentioned he'd provided the citizens with "top-notch maths tuition in a fun but relevant way", among other things. (TV: The Magician's Apprentice)
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)
In mathematics, i was an imaginary number that was the value of the square root of negative one. (AUDIO: Iterations of I)
51 was a pentagonal number. (TV: The Tsuranga Conundrum)
Any number that "reduce[d] to 1 when you take the sum of the square of its digits, and continue[d] iterating it until it yield[ed] 1," was a happy number. (TV: 42)
Types of mathematics
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, numbers which are both happy and prime. He seemed surprised it wasn't a regularly studied course. (TV: 42)