 # Factorial Notation

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The expression 6 × 5 × 4 × 3 × 2 × 1 = can be written as 6!, which is read as “six factorial.”

In general, n! is the product of all the counting numbers beginning with n and counting backwards to 1. We define 0! to be 1.

The following diagram describes the factorial notation and gives some examples using factorials. Scroll down the page for more examples and solutions using factorials. Example:

Find the value of each expression:
a) 3!
b) 0!
c) 5!
d) 1!
e) 3! + 2!
f) Solution:

a) 3! = 3 × 2 × 1 = 6
b) 0! = 1
c) 5! = 5 × 4 × 3 × 2 × 1 = 120
d) 1! = 1
e) 3! + 2! = (3 × 2 × 1) + (2 × 1) = 8
f) Factorials Explained! Some basic information on factorials and shows how to evaluate some factorial examples.

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