## `numlib::fibonacci` -- Fibonacci numbers

#### Introduction

`numlib::fibonacci``(n)` returns the `n`-th Fibonacci number.

#### Call(s)

`numlib::fibonacci(n)`

#### Parameters

`n` | - | a nonnegative integer

#### Returns

a nonnegative integer, or the function call with its arguments evaluated.

#### Details

- If `n` is a nonnegative integer then `numlib::fibonacci``(n)` returns the `n`-th Fibonacci number.
- `numlib::fibonacci` returns an error if the argument evaluates to a number of wrong type. `numlib::fibonacci` returns the unevaluated function call if `n` does not evaluate to a number.

#### Example 1

We compute the -the Fibonnacci number:

    >> numlib::fibonacci(201)

                    453973694165307953197296969697410619233826

#### Background

- The n-th Fibonacci number Fn is defined by the recursion formula F0=0, F1=1, and Fn+2 = Fn + Fn+1 .
- `numlib::fibonacci` uses quadratic recursion formulas.

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