Factorial Calculator
Find the factorial of any number between 1 and 170. For help in using the
calculator, read the FrequentlyAsked Questions
or review the Sample Problem.
 Enter a number in the unshaded text box.
 Click the Calculate button to display
the factorial value of that number.




Instructions: To find the answer to a frequentlyasked
question, simply click on the question.
What is a factorial?
In general, n objects can be arranged in n(n
 1)(n  2) ... (3)(2)(1) ways. This product is represented by the
symbol n!, which is called n factorial. By convention, 0! = 1.
Thus, 0! = 1; 2! = (2)(1) = 2; 3! = (3)(2)(1) = 6; 4! =
(4)(3)(2)(1) = 24; 5! = (5)(4)(3)(2)(1) = 120; and so on.
Factorials can get very big, very fast. The term 170! is the
largest factorial that the Factorial Calculator can evaluate. The term 171! produces a
result that is too large to be processed by this software; it is bigger than 10
to the 308th power.
For an example that computes a factorial, see
Sample Problem 1.
What is ENotation?
E notation is a way to write numbers that are too large or
too small to be concisely written in a decimal format.
With E notation, the letter E represents "times ten raised to the
power of". Here is an example of a number written using E notation:
3.02E12 = 3.02 * 10^{12} = 3,020,000,000,000
The Factorial Calculator uses E notation to express very
large numbers. For example, the term 170! is expressed in E notation as
7.25741561530799E+306.
How accurate is ENotation?
If the Factorial Calculator displays a result in E notation,
that result is not exact. It is an approximation, accurate to within
16 significant digits.

A standard deck of playing cards has 13 spades. How many
ways can these 13 spades be arranged?
Solution:
The solution to this problem involves calculating a factorial. Since we want to
know how 13 cards can be arranged, we need to compute the value for 13
factorial.
13! = (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) = 6,227,020,800
Note that the above calculation is a little cumbersome to compute by hand, but
it can be easily computed using the Factorial Calculator. To use the
Factorial Calculator,
do the following:
 Enter "13" for n.
 Click the "Calculate" button.
The answer, 6,227,020,800, is displayed in the "n Factorial"
textbox.