In this video I present optimal computer generated solutions for designing 1:N (N=prime) ratios using a single Lego Technic differential. Insights and ideas are shown for implementing the 1:N designs in practice using Lego Technic liftarms with an example 421:1 gear ratio device. All the possible solutions for N less than 1000 are shown and can be used in your own Lego Technic MOC designs if you are needing to create a particular gear ratio.