64 (number) it is possible to find sequences of 64 consecutive integers such that each inner member shares a factor with either the first or the last member, 64 is an Erdős–Woods number. In base 10, no integer added up to its own digits yields 64, hence it is a self number. 64 is a superperfect number—a number such that σ(σ("n")) = 2"n". 64 is the index of Graham's number in the rapidly growing sequence 3↑↑↑↑3, 3 ↑ 3,… Sixty-four is: 64 (number) 64 (sixty-four) is the natural number following 63 and preceding 65. Sixty-four is the square of 8, the cube
Square-free integer common divisor of the polynomial and its formal derivative). A positive integer "n" is square-free if and only if in the prime factorization of "n", no prime factor occurs with an exponent larger than one. Another way of stating the same is that for every prime factor "p" of "n", the prime "p" does not evenly divide "n" / "p". Also "n" is square-free if and only if in every factorization "n" = "ab", the factors "a" and "b" are coprime. An immediate result of this definition is that all prime numbers are square-free. A positive integer "n" is square-free