Minecraft wiki entry for Clock, associated text: A T flip-flop can be used to double the period of any clock. This also converts the pulse to have the same length ON and OFF, if it didn't before. (Pseudoclocks are not completely regularized, but they get smoothed out.)
Latched repeaters allow production of a general clock multiplier, detailed below. This can be used to multiply the period of any clock, and they can be used in series.