Find # of Unique Numbers in Large Table

[ExcelAtEverything]

Inside of a very large 300k row table, I have a column containing 300k cells (C2:C300000) each containing a 10-digit number. I'm wondering if there's a faster and less CPU-intensive method for counting the number of unique numbers in that column. I've tried several methods now, but each seems to slow my computer down more than the last. The most recent formula I tried from the web =SUMPRODUCT(1/COUNTIF(C2:C300000,C2:C300000)) pretty much slowed my computer to a dead stop. Is there a faster/more efficient way to retrieve that number?

 

[cadafi]

@cadafi the UNIQUE function is only available in the 365 version of office, not 2016 or 2019.
And as the OP is using 2019 it's not much help.

@Fluff, Sorry I forgot it.
So there are some alternative approach that you can use Pivot-Table, or advance filter to extract the unique list then count it, in stead of using VBA or Array formula.

 

[ExcelAtEverything]

@Fluff, Sorry I forgot it.
So there are some alternative approach that you can use Pivot-Table, or advance filter to extract the unique list then count it, in stead of using VBA or Array formula.

Thanks Cadafi! Pivot Tables are the route I chose to go. In a separate thread topic where I was looking for options for my data-heavy CPU-stressed sheet, RoryA suggested to me that I could create a connection only query and use that as the data source for pivot tables, & that I could then load it to the data model and use Power Pivot. So that is exactly what I did. Although I'm still getting thru it (as I'm still a newb & only a couple of weeks old on both Power Query & Pivot Tables), switching to PT's using a data model eliminated any lags in my sheet, and it is lightning fast now. Pivot Tables definitely a much better option for large data sets like what I have here.
--> Link to that thread if anyone is interested: (Reaching Excel's Limits)