Numerology

Numerology is a magical discipline relating to numbers that appears to be part of, similar to, or related to Arithmancy.

Presumably taught by Septima Vector in Arithmancy at Hogwarts School of Witchcraft and Wizardry, books on the subject include Numerology and Grammatica and New Theory of Numerology.

Appearances

 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Order of the Phoenix