Yes. The formula for A weighting at any frequency in dB is given by
=10*LOG10(B11^8/((B11^2+20.6^2)^2*(B11^2+12200^2)^2*(B11^2+107.7^2)*(B11^2+737.9^2)))+165.45
where B11 contains the frequency in Hz
I've checked this against the standard for each 1/3 oct centre frequency Cheers
Greg Locock