## Number Theory

Factor
to factor means to write as a product
Factor 6
$6 = 2 \cdot 3$

When factoring, it is often useful to list only the prime factors. Usually, we do not list 1 as a factor.

Prime
A prime number is a natural number (positive, whole) only divisible by 1 and itself. A prime number must also be greater than 1. 2 is the first prime number. 2 is the only even prime number.
Composite
A composite number is a natural number greater than 1 that is not prime.
Factor 26
$2 \cdot 13$
Factor 125
$5 \cdot 5 \cdot 5$
Least common multiple (lcm)
The least common multiple of two numbers is the smallest number evenly divisible by both numbers (no remainder).

The least common multiple of 3 and 6 is 6.

What is the least common multiple of 3 and 4? Write out several multiples until a number matches both.