# isnan proc

Source: https://ref.dm-lang.org/proc/isnan
Added in BYOND 515.

### Format
> `isnan(n)`

### Args
> n: A number

### Returns
> 1 if this is a numeric value but is an invalid "not a number" (NaN); 0 otherwise

Some math operations return the special number `NaN` if they're undefined, such as dividing 0 by 0. This tells you if a number is that type.

NaN is never greater than, less than, or equal to another number, even itself.

### See also
- [isnum proc](https://ref.dm-lang.org/proc/isnum.md)
- [isinf proc](https://ref.dm-lang.org/proc/isinf.md)
- [Numbers](https://ref.dm-lang.org/notes/numbers.md)