The Excel NA function returns the #N/A error. #N/A means “not available” or “no value available”.
Use NA to generate the #N/A. #N/A means “not available” or “no value available”. For example, you can use NA to flag cells that are empty or missing information.
When other formulas refer to cells that contain #N/A, the also return #N/A.
NA takes no arguments, but you must provide empty parentheses.
You can also enter the value #N/A directly into a cell.