Let a divisor of be called a 1-ary (or unitary) divisor if (i.e., is relatively prime to ). Then is called a -ary divisor of , written , if the greatest common -ary divisor of and is 1 (Cohen 1990).
In this notation, is written , and is written .
is an infinitary divisor of (with ) if .
Suryanarayana (1968) unfortunately uses a different and conflicting definition.