The

unitary divisors of an

integer *n* are those pairs of integers

*a* and

*b* satisfying

*ab = n* and

*(a,b) = 1*.

^{*}
For example, the unitary divisors of 99 are 1, 9, 11 and 99 (but not 3 or 33).

^{*}Here *(a,b)* denotes, as usual, the greatest common divisor of *a* and *b*; thus, the condition *(a,b) = 1* means that *a* and *b* have no factors in common which are greater than 1.