Consider hex and base 64. Base 16 takes the first six letters from the alphabet to augment the number of available letters for representing a particular value.

Consider hex and base 64. Base 16 takes the first six letters from the alphabet to augment the number of available letters for representing a particular value. I guess using base 26 would make sense from a strictly alphabetic standpoint, but we've conventionally included the numbers 0-9 as part of the available letters for representation.