# 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.