Full Idea
Number is the determinant of individual being.
Gist of Idea
Number determines individual being
Source
Plotinus (The Enneads [c.245], 5.1.05)
Book Reference
Plotinus: 'The Enneads', ed/tr. Mackenna,Stephen [Penguin 1991], p.352
A Reaction
You might have thought that number was the consequence of the individualities (or units) within being, but not so. You can't get more platonic than saying that the idealised numbers are the source of the particular units.