That seems like it should work. You would then use =FINDME(M1) in some other cell (like N1).

I put the numbers 1 through 20 in L6:L25, then various numbers in M6:M25 (some duplicates). If I put one of the numbers from M6:M25 into M1, N1 returns the proper references from L6:L25. If I put a number in M1 that does not exist in M6:M25 then N1 is blank.