Number of stakeholders?

How do I derive number of stakeholders when I am given a number of communication channels only?

For example, what would be the number of stakeholders if the number of communciation channels is 30?

I usually do by implying the options one by one in the formula. i know it consumes time. but it is easy.

Agree - just try one by one. 

It is also possible to solve a quadratic equation to find a formula. I knew how to do that long time ago, when i was 14. But not now(

since 8 stakeholders have 28 channels and 9 stakeholder have 36, you'd need to cut some people up?