Hello, this formula works for column C - I just modified it slightly to begin at cell C21. Thank you! That said, can you help with column B (which actually starts with B21)? I tried to modify what you provided for C as follows:

=AND(MEDIAN(CODE(LEFT(B21,1)),65,90)=CODE(LEFT(B21,1)),MEDIAN(CODE(MID(B21,2,1)),65,90)=CODE(MID(B21,2,1)),ISNUMBER(RIGHT(B21,2)+0),LEN(B21)=4)

However, I am sure I missed something. Column B example is: N1234 - First character is alpha value and the next four characters are numeric values.