There is no ideal number of repetitions. It is very personal and highly dependent on the individual response to training.
However, in a workout aimed at gaining strength, the repetitions are lower and the intensities are higher... you can work between 1 to 6 at 75% to 105%.
However I believe that the scheme of repetitions and intensities should vary a little more. In off season I work at a much larger volume and work with repetitions between 5 and 15... and yet my ultimate goal remains the strength gain to lift more weight.