repdigit

It is also the smallest odd repdigit that is not a prime number.

The word repdigit is a portmanteau, formed from repeated digit.

It is a decimal repdigit and a strobogrammatic number (meaning that it looks the same turned upside down on a calculator display).

In recreational mathematics, a repdigit or sometimes monodigit is a natural number composed of repeated instances of the same digit in a positional number system (often implicitly decimal).