Definition:Amicable Pair/Definition 1

Definition
Let $m \in \Z_{>0}$ and $n \in \Z_{>0}$ be (strictly) positive integers. $m$ and $n$ are amicable numbers :
 * the aliquot sum of $m$ is equal to $n$

and:
 * the aliquot sum of $n$ is equal to $m$.

Also see

 * Equivalence of Definitions of Amicable Numbers