What is the frequency to EQ a certain note?

The fundamental frequency fn of the particular note is:

fn = f0 * a * n

f0 = A above middle C (A4 = 440 Hz).

n = amount of half notes removed from A4. N>0 for notes higher than A4 en N<0 for notes lower than A4. the fixed value a = (2)1/12 = = 1.059463094

Things become easier if you use the table. If you play a note one octave higher, the frequency doubles. For instance if your note E2 is not loud enough compared to all other notes. You have to EQ the frequency of E2:

in the table you find that E0 = 20.60

So E2 is: E2= 20.60 * 2 * 2= 82.4 Hz

The wave length does just the opposite. One octave higher means half the wavelength.