Prime Numbers.
Just as writing and speaking uses letters and words to express meaning and ideas, math uses numbers and symbols.

You may remember that numbers may be EVEN: (0, 2, 4, 6, 8)
and ODD: (1, 3, 4, 7, 9)

They may also be:
Greater than Zero (Positive); N > 0
ZERO has no sign. It is neither positive or negative.
Less than Zero (Negative); N < 0

A FACTOR of a number is a value that can be divided into the number evenly (without a remainder).
Since Multiplication is the opposite if Division, we sometimes say: Two numbers that multiply together to make a product are factors of a number.

Factors are considered to be WHOLE Numbers (no Decimals and Fractions).
For example: factors of  SIX (6) are:  1 x 6 and 2 x 3.

While 6 = 1.5 x 4, at this time, 1.5 is not considered a factor.
Zero is also not a factor since division by zero: Number/0 is Undefined. 
The opposite of Division is Multiplication and Zero x (any number) is zero.

Composite Numbers have more than 2 Factors.
Prime Numbers only have 2 Factors (1 and Itself)
ZERO: Neither Prime nor Composite: Infinite number of factors
ONE: Neither Prime nor Composite: only one factor: 1 x 1
TWO: Prime: 1 x 2.  Is the only only EVEN Prime Number.
THREE: Prime: 1 x 3
FOUR: Composite:  1 x 4, 2 x 2 (3 factors)
FIVE: Prime: 1 x 5
SIX: Composite: 1 x 6, 2 x 3
SEVEN: Prime: 1 x 7
EIGHT: Composite: 1 x 8, 2 x 4
NINE: Composite: 1 x 9, 3 x 3 (3 factors)
TEN: Composite: 1 x 10, 2 x 5
ELEVEN: Prime: 1 x 11
TWELVE: Composite: 1 x 2, 2 x 6, 3 x 4
THIRTEEN: Prime: 1 x 13
FOURTEEN: Composite: 1 x 14, 2 x 7
FIFTEEN: Composite: 1 x 15, 3 x 5
SIXTEEN: Composite: 1 x 16, 2 x 8, 4 x 4
SEVENTEEN: 1 x 17
EIGHTEEN: 1 x 18, 2 x 9, 3 x 6 
NINETEEN: Prime: 1 x 19
TWENTY: Composite: 1 x 20, 2 x 10, 4 x 5

What pattern is there? 
Zero and One are neither Prime or Composite!
ALL PRIME NUMBERS ARE ODD (ACCEPT '2').
EVEN NUMBERS ARE NEVER Prime (Accept 2).
Prime Numbers only have two factors: 1 and itself.
All Composite Numbers are made up of the Product of Primes.
Six (6) is 2 x 3
Eight (8) is 2 x 4; (but 4 is 2 x 2)  so; 8 = 2 x (2 x 2)

Knowing your DIVISIBILITY RULES: will help to quickly identify primes.
Divisible by '3' Sum of the Digits
Divisible by '5' Ends in Zero or Five

Revised: April 29, 2024