Cube (algebra) however, easy to show that most numbers are not perfect cubes because "all" perfect cubes must have digital root 1, 8 or 9. That is their values modulo 9 may be only −1, 1 and 0. Moreover, the digital root of any number's cube can be determined by the remainder the number gives when divided by 3: Every positive integer can be written as the sum of nine (or fewer) positive cubes. This upper limit of nine cubes cannot be reduced because, for example, 23 cannot be written as the sum of fewer than nine positive cubes: The equation has
USS Apache (SP-729) June 1917. She was commissioned as USS "Apache" (SP-729) at Boston on 7 July 1917. "Apache" served as a dispatch boat and local patrol boat at Boston, operating under the aegis of the 1st Naval District, through early October 1918, by which time her name had been changed to USS "SP-729". Due to an urgent need for craft such as "SP-729" at Brest, France, an order dated 14 October 1918 went out from Washington, D.C., to Boston, directing the Commandant of the 1st Naval District to ready six section patrol boats -- USS "Commodore" (SP-1425), USS "Cossack" (SP-695), USS "War