unary numeral system

The unary numeral system is the bijective base-1 numeral system. It is the simplest numeral system to represent natural numbers: in order to represent a number N, an arbitrarily chosen symbol representing 1 is repeated N times. For examples, the numbers 1, 2, 3, 4, 5, ... would be represented in this system as

1, 11, 111, 1111, 11111, ...

These numbers should be distinguished from repunits, which are also written as sequences of ones but have their usual decimal numerical interpretation.