Is there a formula to restrict counting ID once?

In my sheet, I have a column that counts the number of extensions for each request. I would like my sheet summary to show the number of of requests that have been extended once, twice, three times, etc. The number of requests extended once was easy to formulate since the request is only referenced once (=COUNTIF([Number of Extensions]:[Number of Extensions], 1). However, I'm having problems correctly counting those with ID's that repeat. Is there something I can add to the formula that would only count Request ID's once even though there are multiple rows with that ID?) Would there be a better way to set up?



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