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) Bug" (SP-1795), USS "Sea Hawk" (SP-2365), USS "Kangaroo" (SP-1284), and "SP-729"—to be shipped to France as deck cargo along with spare parts to keep them operational. However, this proposed movement appears to have been cancelled, probably because of the armistice with Germany of 11 November 1918 that ended World War I and eliminated the need for more U.S. Navy patrol craft in Europe. Instead, "SP-729" headed south via the inland waterway in December 1918, bound for Naval Air Station Pensacola at Pensacola, Florida, probably for duty as a crash boat. "SP-729" was decommissioned at Key West, Florida, and stricken from