I'm looking for a formula that will search a list to see if it is a date.  I have a list of numbers as follows:

M05899
M06125
L15214
013114
M06828
M06901

From the list above 013114 is a date and the other strings are invoice numbers.  In particular I would like to know if the date listed is the last date of any particular month or year.  In other words it should not be any date, but specifically the last date of any month or year.  I believe this may be done with an if and then type of clause but wondering if there is a better way.  I couldn't find a date function in the formula editor that would do this.  Any help would be greatly appreciated.

Thank you very much! You're awesome!

Edited by jack123 - 27 Apr 2015 at 5:24am