Persistence of a number assumed. The single-digit final state reached in the process of calculating an integer's additive persistence is its digital root. Put another way, a number's additive persistence counts how many times we must sum its digits to arrive at its digital root. The additive persistence of 2718 is 2: first we find that 2 + 7 + 1 + 8 = 18, and then that 1 + 8 = 9. The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4. Also, 39 is the smallest
128 (number) vertices. 128 is the only 3-digit number that is a 7th power (2). One hundred [and] twenty-eight is also: 128 (number) 128 (one hundred [and] twenty-eight) is the natural number following 127 and preceding 129. 128 is the seventh power of 2. It is the largest number which cannot be expressed as the sum of any number of distinct squares. But it is divisible by the total number of its divisors, making it a refactorable number. The sum of Euler's totient function φ("x") over the first twenty integers is 128. 128 can be expressed by a combination of its digits