Some options...

1]

=SUM(IF(A2:A100<"",1/COUNTIF(A2:A100,A2:A100)))

which must be confirmed with control+shift+enter intead of just with enter.

2]

=SUMPRODUCT((A2:A100<"")/COUNTIF(A2:A100,A2:A100&""))

3]

=SUM(IF(FREQUENCY(A2:A10,A2:A10)0,1))

The last two just need enter.

Alex wrote:
If I have a column with some repeated numbers:

58
168
168
25
...

How could I count the cells from the column to get 3 (not 4) as a result -
to be able to count the one number only once.

Thanks