Prime number

A prime number was a number with special properties.

The Tenth Doctor could quickly compute happy primes to get access to computer systems. He claimed that happy primes were studied in recreational mathematics. (TV: 42)

April MacLean mistook prames of the Renyalin, known from the planet Rhodia, for primes. (PROSE: The Stone House)

Mrs Multravers tested intelligence of humans by asking them a question about prime numbers. (AUDIO: The Haunting)

Behind the scenes
A prime number is a positive integer that has exactly two divisors: 1 and the number itself.