Experimental results of pleasing two note combinations (consonances) are given in Juan Roederer's 'The Physics and Psychophysics of Sound'. Within 75% confidence limits, any two notes are consonant if the ratio of their frequencies is between a minor third (6/5 ratio) and a major 5th (3/2) ratio. It's easy to apply the same ratios again with the higher of the two frequencies to find the range of frequencies that a third note can have, so you have a chord. 335 Hz and 440 Hz fit well within the limits of a consonance.