Repunit

A repunit in base 10 is a number consisting only of the digit 1: 1, 11, 111, 1111, … The name is short for "repeated unit".

Key features

• In base 10, repunits have the form (10^n − 1)/9.
• Repunit primes (2, 19, 23, … digits) are of interest in number theory.

Examples:

1, 11, 111, 1111, 11111

Further reading

• Repunit on Wikipedia
• Repunit on OEIS