Number

Numbers were studied in mathematics.

Certain numbers had certain properties. For example, the Tenth Doctor once stated that 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. Moreover, if such number was also prime, it was called a happy prime. (TV: 42)

51 was a pentagonal number. (TV: The Tsuranga Conundrum)

In mathematics, 𝑖 was an imaginary number that was the value of the square root of negative one. (AUDIO: Iterations of I)

In place of names, Dalek soldiers could be designated with a number by their superiors, such as those constructed on Vulcan (e.g. Dalek 17, Dalek 18) (TV: The Power of the Daleks) and those who invaded Trodos. (COMIC: The Trodos Ambush) The Space Security Service also assigned numbers to Daleks they had captured. (COMIC: The Only Good Dalek)