Im trying to find a formula (maybe, IF function even though i've tried a few) to show:

Item No. of
1234
2345 2
2345 2
3456
4567
5678 3
5678 3
5678 3

Basically it needs to show how many "item" numbers are the same (in the "no. of" column) but if only a single "item" number i'd like the "no. of" column to be blank. Any help would be greatly appreciated.