Definition:Repdigit Number

Definition
Let $b \in \Z_{>1}$ be an integer greater than $1$.

Let a (positive) integer $n$ be expressed in base $b$.

$n$ is a repunit base $b$ all of the digits of $n$ are the same digit.

For example:
 * $55555$

or:
 * $3333_4$

that second one being in base 4.