Wrong. 20MHz is the channel width (bonded together to make 40, 80 and 160MHz aggregate channels). There are three non-overlapping channels in the 2.4GHz band (so 60) and "many" in the existing 5GHz allocation. In some countries there's an extra usable channel in 2.4GHz. Once you bloat up to 160MHz (which is needed to achieve the highest marketing speeds) it is hard to find clear gaps in today's 5GHz because it isn't contiguous.