5 (number)

5 was a prime number. (AUDIO: The Haunting)

In November 1963, Susan Foreman said that the last five months had been the happiest of her life (indicating that was how long she had been living in England). (TV: "An Unearthly Child") In March of that year, Susan wrote in her journal that they'd been in 1963 for five months, or at least it seemed like it. (PROSE: Time and Relative)

Upon meeting the Fifth Doctor, the First Doctor exclaimed "goodness me!" as he realised that he now had five incarnations. Elsewhere, an illusionary Liz Shaw told the Third Doctor that there were now five of him, to which he exclaimed "oh, good grief." (TV: The Five Doctors)

In an emergency transmission sent by the TARDIS, the Thirteenth Doctor listed 5 things that she did in any worrying situation. The fifth was staying strong and to stay positive. (WC: Message from the Doctor)