In general, a number or algebraic expression 
is a factor (or divisor) of another 
if there exists a number or algebraic expression 
of a specified type for which 
A natural number 
is a factor of a natural number 
if there is a natural number such that 
For example, 
is a factor of 12 because 
A polynomial 
is divisible by a polynomial 
if there is a polynomial 
for which 
For example, 
is a factor 
because 
.
A prime factor of a natural number is a factor of that is a prime number.
For example, the prime factors of 
are 