# isSquareTriangularNumber
> Test if a value is a [square triangular number][square-triangular-number].
A **square triangular number** is an integer value which is both a [square number][@stdlib/assert/is-square-number] and a [triangular number][@stdlib/assert/is-triangular-number].
[Triangular numbers][@stdlib/assert/is-triangular-number] can be computed using the following formula
for `n >= 0`.
By analogy with the square root of `x`, one can define the positive triangular root of `x` such that `T_n = x`
Accordingly, an integer `x` is a [triangular number][@stdlib/assert/is-triangular-number] **if and only** if `8x+1` is a [square number][@stdlib/assert/is-square-number].
## Usage
```javascript
var isSquareTriangularNumber = require( '@stdlib/assert/is-square-triangular-number' );
```
#### isSquareTriangularNumber( value )
Tests if a `value` is a [square triangular number][square-triangular-number].
```javascript
var Number = require( '@stdlib/number/ctor' );
var bool = isSquareTriangularNumber( 36.0 );
// returns true
bool = isSquareTriangularNumber( new Number( 36.0 ) );
// returns true
bool = isSquareTriangularNumber( 3.14 );
// returns false
bool = isSquareTriangularNumber( -5.0 );
// returns false
bool = isSquareTriangularNumber( NaN );
// returns false
bool = isSquareTriangularNumber( null );
// returns false
```
#### isSquareTriangularNumber.isPrimitive( value )
Tests if a `value` is a primitive [square triangular number][square-triangular-number].
```javascript
var Number = require( '@stdlib/number/ctor' );
var bool = isSquareTriangularNumber.isPrimitive( 36.0 );
// returns true
bool = isSquareTriangularNumber.isPrimitive( new Number( 36.0 ) );
// returns false
```
#### isSquareTriangularNumber.isObject( value )
Tests if a `value` is a `Number` object having a value which is a [square triangular number][square-triangular-number].
```javascript
var Number = require( '@stdlib/number/ctor' );
var bool = isSquareTriangularNumber.isObject( 36.0 );
// returns false
bool = isSquareTriangularNumber.isObject( new Number( 36.0 ) );
// returns true
```
## Notes
- Return values are not reliable for numbers greater than `1125899906842624`.
## Examples
```javascript
var Number = require( '@stdlib/number/ctor' );
var isSquareTriangularNumber = require( '@stdlib/assert/is-square-triangular-number' );
var bool = isSquareTriangularNumber( 36.0 );
// returns true
bool = isSquareTriangularNumber( new Number( 36.0 ) );
// returns true
bool = isSquareTriangularNumber( 0.0 );
// returns true
bool = isSquareTriangularNumber( 1.0 );
// returns true
bool = isSquareTriangularNumber( 3.14 );
// returns false
bool = isSquareTriangularNumber( -5.0 );
// returns false
bool = isSquareTriangularNumber( NaN );
// returns false
bool = isSquareTriangularNumber( '0.5' );
// returns false
bool = isSquareTriangularNumber( null );
// returns false
```
[square-triangular-number]: https://en.wikipedia.org/wiki/Square_triangular_number
[@stdlib/assert/is-square-number]: https://www.npmjs.com/package/@stdlib/assert/tree/main/is-square-number
[@stdlib/assert/is-triangular-number]: https://www.npmjs.com/package/@stdlib/assert/tree/main/is-triangular-number
