The original "logic" of the numbering was that the prefix referred to the power of one-million, which is the same as the number of six-zero groupings.
Million = 10^6 = 1,000,000
Billion = (10^6)^2 = 10^(6*2) = 1,000,000,000,000
Trillion = 10^(6*3) = 1,000,000,000,000,000,000
Quadrillion =...