A

counting

system that uses only one

digit. The places in the system
follow the same rules as all other

counting systems. The

number
5 is represented in unary as:

11111

which

translates to:

1

^{4}+1

^{3}+1

^{2}+1

^{1}+1

^{0}
However, this yields: `1 + 1 + 1 + 1 + 1 = 5`. Much less
interesting than other number systems.

Prime numbers in unary have an interesting property that allows them to
be matched by the following perl regular expression:

`perl -le '{(1 x ++$_) !~ /^(11+)\1+$/ && print; redo}'`

Compare to binary or decimal