13th root 13th root Extracting the 13th root of a number is a famous category for the mental calculation world records. The challenge consists of being given a large number (possibly over 100 digits) and asked to return the number that, when taken to the 13th power, equals the given number. For example, the 13th root of 8,192 is 2 and the 13th root of 96,889,010,407 is 7. Extracting the 13th root has certain properties. One is that the 13th root of a number is much smaller: a 13th root will have approximately 1/13th the number of digits. Thus, the 13th root
Digital root number is a positive integer if and only if the number is itself a positive integer. The digital root of formula_1 is formula_1 itself if and only if the number has exactly one digit. The digital root of formula_1 is less than formula_1 if and only if the number is greater than or equal to 10. The digital root of formula_45 + formula_46 is digital root of the sum of the digital root of formula_45 and the digital root of formula_46. The digital root of formula_45 - formula_46 is congruent with the difference of the digital root of formula_45 and