tuning/pitching resonant filters, need help with [expr]

Hi
I am separately tuning a resonant filter and an IIR delay line, to give a 2 octave scale. Using my ears I've got 520Hz for middle C, 1040Hz for the octave above and 2080Hz for the next C above that. For the delay line I've got 132, 264 and 530 for the same pitches.

Can anyone work out the expression I need to use on a single integer/float input to give me those values; ie 520=132, 1040=264, etc. It is almost doubling every octave, but I'm aware that we hear pitch frequencies on a logarithmic scale. I'm not too concerned with precision, just an approximation.

Thanks
Brendan