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
Hull classification symbol digit of the number is determined by the ships "power tonnage," defined as the sum of its shaft horsepower and gross international tonnage, as follows: The second and third digits are assigned to create a unique three-digit hull number. Hull classification symbol The United States Navy, United States Coast Guard, and United States National Oceanic and Atmospheric Administration (NOAA) use a hull classification symbol (sometimes called hull code or hull number) to identify their ships by type and by individual ship within a type. The system is analogous to the pennant number system that the Royal Navy and other European