1. Numbers are abstract or concrete. The latter are divided as
follows: first, lineal; second, superficial; third, solid. Abstract
number is that which is made up of abstract units. For example, III,
IV, V, VI, and so on.
2. Concrete number is that which is made up of units that are not
abstract, as for example, the number three, if it is understood of
magnitude, whether line, superficies, or solid, is called concrete.
4. The number of superficies is that which is constituted not only by
length but also by breadth, as triangular, square, pentangular, or
circular numbers, and the rest that are contained in a plane surface
or superficies.
5. The circular number, when it is multiplied by itself, beginning
with itself, ends with itself. For example, _Quinquies quini vicies
quinque_.
6. ... The spherical number is that which being multiplied by the
circular number begins with itself and ends with itself; for example,
five times five are twenty-five, and this circle being multiplied by
itself makes a sphere, that is, five times XXV make CXXV.