II.1 chapter 30

Are the works of God (which came forth from the unchangeable Word of God) an imperfect reality?
No, they are still a perfect reality. This is signified by the number of days in which the world was made: in six days, where the number six is the first perfect number (perfect numbers are sparse: following are 28, 496, 8128, 33550336, ...).

(And therefore we must not despise the science of numbers, which, in many passages of holy Scripture, is found to be of eminent service to the careful interpreter.)