How do you write nan in Greek?

There isn't a direct translation of "NaN" (Not a Number) in Greek that captures the same technical meaning. NaN is a specific computer science concept. You would need to explain the concept in Greek, likely using a phrase like:

* Μη αριθμός (Mi arithmos): This translates literally to "Not a number," and is the closest direct equivalent, although it might lack the nuanced meaning of NaN in a computational context.

* Μη ορισμένος αριθμός (Mi orismenos arithmos): This means "Undefined number," which might be more appropriate in certain contexts where the value is indeterminate.

* Απροσδιόριστη τιμή (Aprospidioristi timi): This translates to "Undefined value," which is a broader term that could encompass NaN but also other undefined data types.

The best choice depends on the specific context. For technical documents or programming, a brief explanation alongside one of these phrases might be necessary to ensure clarity.