Didascalicon, Book II: the sciences, their parts and their discipline
Chapter XII. On arithmetic
Arithmetic has as its matter the even and the odd number. Of even number, one is evenly even, another evenly odd, another oddly even. Odd number, too, has three species. The first is prime and incomposite; the second is secondary and composite; the third is secondary of itself and composite and compared with others: prime and composite.