Formula for validating text in cell with pattern of numbers and letters

Hi,

I am looking out for a excel formula that helps me to find out the cells that has first four characters as numbers and next two characters as letters. Eg - 1234AB. I have a list in column A that has only letters and only numbers and alphanumeric cells and a few cells in the above format of 1234AB etc. I want a formula that identify such cells out of the list. Can anyone help please?