Introduction to Arithmetic

Nicomachus of Gerasa · ~100 d.C.

A Neopythagorean manual that classified numbers by their qualities (perfect, abundant, deficient) and influenced all later numerology.

It divides numbers into classes by their relationship with the sum of their divisors — the so-called perfect numbers. That vocabulary (perfect, abundant, deficient) passed into the esoteric tradition.

Nicomachus is the route by which Pythagorean arithmetic reached Europe. His treatment of numbers as entities with 'virtues' is the technical root of many concepts numerology uses today.