Excel Data Validation
1. cell value contain 4 character only and left two character is EE and last two character is digit and can not support duplicate value. go to data tab-->validation-->ALLOW[custom] and type following formula =AND(LEN(B1)=4,LEFT(B1,2)="EE",COUNTIF($B$1:$B$76,B1)<2,ISNUMBER(VALUE(RIGHT(B1,2)))) 2.