# factorial

Factorial of symbolic input

## Syntax

``f = factorial(n)``

## Description

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````f = factorial(n)` returns the factorial of `n`. If `n` is an array, `factorial` acts element-wise on `n`.```

## Examples

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Compute the factorial for a symbolic number.

`f = factorial(sym(20))`
`f = $2432902008176640000$`

Compute the factorial function for a symbolic expression. `factorial` returns exact symbolic output as the function call.

```syms n expr = n^2 + 1; f = factorial(expr)```
`f = $\left({n}^{2}+1\right)!$`

Calculate the factorial for a value of `n = 3`. Substitute the value of `n` by using `subs`.

`fVal = subs(f,n,3)`
`fVal = $3628800$`

Differentiate an expression containing the factorial function $\left({\mathit{n}}^{2}+\mathit{n}+1\right)!$

```syms n f = factorial(n^2 + n + 1)```
`f = $\left({n}^{2}+n+1\right)!$`
`df = diff(f)`
`df = $\left({n}^{2}+n+1\right)! \psi \text{psi}\left({n}^{2}+n+2\right) \left(2 n+1\right)$`

The derivative of the factorial function is expressed in terms of the `psi` function.

Expand an expression containing the factorial function.

```syms n f = factorial(n^2 + n + 1); f1 = expand(f)```
`f1 = $\left({n}^{2}+n\right)! \left({n}^{2}+n+1\right)$`

Compute the limit at infinity for an expression containing the factorial function.

```syms n f = factorial(n)/exp(n); fLim = limit(f,n,Inf)```
`fLim = $\infty$`

Compute factorial for array input. `factorial` acts element-wise on array input.

```A = sym([1 3; 4 5]); f = factorial(A)```
```f =  $\left(\begin{array}{cc}1& 6\\ 24& 120\end{array}\right)$```

## Input Arguments

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Input, specified as a number, vector, matrix, or array, or a symbolic number, variable, array, function, or expression.

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### Factorial Function

The factorial of a number n is defined as follows.

`$n!=\prod _{k=1}^{n}k$`

The factorial of 0 is 1.

## Tips

• Calling `factorial` for a number that is not a symbolic object invokes the MATLAB® `factorial` function.