# Tribonacci
> Compute the nth [Tribonacci number][tribonacci-number].
The [Tribonacci numbers][tribonacci-number] are the integer sequence
The sequence is defined by the recurrence relation
with seed values `F_0 = 0`, `F_1 = 0`, and `F_2 = 1`.
## Usage
```javascript
var tribonacci = require( '@stdlib/math/base/special/tribonacci' );
```
#### tribonacci( n )
Computes the nth [Tribonacci number][tribonacci-number].
```javascript
var v = tribonacci( 0 );
// returns 0
v = tribonacci( 1 );
// returns 0
v = tribonacci( 2 );
// returns 1
v = tribonacci( 3 );
// returns 1
v = tribonacci( 63 );
// returns 8607945812375585
```
If `n > 63`, the function returns `NaN`, as larger [Tribonacci numbers][tribonacci-number] cannot be safely represented in [double-precision floating-point format][ieee754].
```javascript
var v = tribonacci( 64 );
// returns NaN
```
If not provided a nonnegative integer value, the function returns `NaN`.
```javascript
var v = tribonacci( 3.14 );
// returns NaN
v = tribonacci( -1 );
// returns NaN
```
If provided `NaN`, the function returns `NaN`.
```javascript
var v = tribonacci( NaN );
// returns NaN
```
## Examples
```javascript
var tribonacci = require( '@stdlib/math/base/special/tribonacci' );
var v;
var i;
for ( i = 0; i < 64; i++ ) {
v = tribonacci( i );
console.log( v );
}
```
[tribonacci-number]: https://en.wikipedia.org/wiki/Generalizations_of_Fibonacci_numbers#Tribonacci_numbers
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
