Repdigit
In recreational math, a repdigit or a monodigit is a type of natural number. It is only made of the same repeated digit. The word is a portmanteau of repeated and digit. Examples can be numbers like 11, 666, 4444, and 999999. Repdigits are palindromic numbers (read the same forwards and backwards) and are multiples of repunits (a number that only has 1 in it).