Product of GCD and LCM

Theorem

 * $\lcm \set {a, b} \times \gcd \set {a, b} = \size {a b}$

where:
 * $\lcm \set {a, b}$ denotes the lowest common multiple of $a$ and $b$
 * $\gcd \set {a, b}$ denotes the greatest common divisor of $a$ and $b$.