Without some kind of example, I can only guess.
Here's one possible option:
This formula returns the smallest single-occurrence, non-blank value i
the range A1:A15
B1: =MIN(IF(COUNTIF(A1:A15,A1:A15)=1,A1:A15))
Note: Commit that array formula by holding down the [Ctrl][Shift] key
and press [Enter].
Example:
A1: 1
A2: 1
A3: (blank)
A4: (blank)
A5: 2
A6: 3
A7: 4
A8: 5
A9: 6
A10: 7
A11: (blank)
A12: 8
A13: 9
A14: 10
A15: 12
B1: returns 2
Is that what you're looking for?
Regards,
Ro