Power output of push-push and N-push oscillators, what is approximate numbers?

Is there any way to approximately know power output of N-push oscillator at N-th even harmonic?
For multipliers there is fourier approach, what can be used here?

Thanks!

Harmonic levels are totally depended on nonlinearity of the circuit,especially active devices.Therefore nonlinearity in otherwords harmonic levels can not be calculated by hand.