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) USS Apache (SP-729) The third USS "Apache" (SP-729), later USS "SP-729", was an armed motorboat that served in the United States Navy as a patrol vessel from 1917 to 1919. "Apache" was built in 1917 by Herreshoff Manufacturing Company at Bristol, Rhode Island, as the civilian motorboat "Herreshoff No. 311" for Robert F. Herrick of Boston, Massachusetts, who named her "Apache" and intended to offer her to the U.S. Navy for use as a patrol vessel during World War I. The U.S. Navy acquired her from Herrick on 23 May 1917 with a scheduled completion date by Herreshoff of 12