What is the circuit rank of a complete graph?

The circuit rank of a complete graph with n=4 (6 edges)is 3. The circuit rank of a complete graph with n=5 (10 edges)is 5. I think that the circuit rank of a complete graph with n=6 (15 edges) is 10? I think that the circuit rank of a complete graph with n=7 (21 edges) is 15?

I don’t see the pattern.