84 was a number.

According to Jo Grant, three sevens times four were equal to 84. Also, when questioned by the Third Doctor how much was 84 minus 35, she answered 49. (TV: The Claws of Axos)

Cordo's father's weight was eighty-four kilos at the time of his death. (TV: The Sun Makers)

Eighty-four Panjistri were selected for the mission to prevent the end of the universe. (PROSE: Timewyrm: Apocalypse)