Data validation for numbers and text together

Question

How to apply data validation when range is number and text. Column A2: A20 contains text and numbers, data validation does not allow to duplicate entry for numbers and data validation allow to duplicate entry for text.

Answer 1

Use DV with Custom > FormulaIs:

=OR(NOT(ISNUMBER(A2)),COUNTIF($A$2:$A$20,A2)=1)