91 is the smallest positive integer expressible as a sum of two cubes in two different ways if negative roots are allowed (alternatively the sum of two cubes and the difference of two cubes): 91 = 63+(-5)3 = 43+33. (See 1729 for more details). This implies that 91 is the second cabtaxi number.
Well ****adoodledoo. Not a lot of people know that.