The equation used to calculate the resonant frequency of a secondary coil

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Original poster: "mercurus2000" <mercurus2000-at-cox-dot-net> 

Hello, I think I might have asked this before, but I'm looking for the 
equation to calculate the resonant frequency of a secondary coil, I'm not 
look for anything super complex that calculates variables like walls and 
the floor, I'm looking for the most simple equation to calcuate the 
resonant frequency of a coil without anything nearby. I could of swore I 
saw the equation floating around on the net somewhere.
Thanks.
Adam