How to efficiently calculate only the low coefficients of a zero-padded FFT I've got an algorithm that zero pads a sequence to 4N, does an FFT, and only uses the lowest frequency N points out of the generated 4N.

This seems like a lot of wasted work, any ideas how this can be done faster?
If you only a few bins then the following may be very efficient for you:
1. Simply do the DFT of at each frequency you need.
2. Use the Goertzel algorithm for each frequency in question.