@skiedude if you want to make the numbers of planets dependant of your HQ and not count the ones where you have bases then something like HQ^1,1-HQ:
HQ5: 1 extra
HQ10: 3 extra
HQ15: 5 extra
HQ20: 7 extra
HQ25: 9 extra
HQ30: 12 extra
Or simpler: 1 + 2 for every 5 HQ levels