64 (number) 64 (number) 64 (sixty-four) is the natural number following 63 and preceding 65. Sixty-four is the square of 8, the cube of 4, and the sixth power of 2. It is the smallest number with exactly seven divisors. It is the lowest positive power of two that is adjacent to neither a Mersenne prime nor a Fermat prime. 64 is the sum of Euler's totient function for the first fourteen integers. It is also a dodecagonal number and a centered triangular number. 64 is also the first whole number that is both a perfect square and a perfect cube. Since
Integer square root which makes a general multiplication step unnecessary. Integer square root In number theory, the integer square root (isqrt) of a positive integer "n" is the positive integer "m" which is the greatest integer less than or equal to the square root of "n", For example, formula_2 because formula_3 and formula_4. One way of calculating formula_5 and formula_6 is to use Newton's method to find a solution for the equation formula_7, giving the iterative formula The sequence formula_9 converges quadratically to formula_5 as formula_11. It can be proven that if formula_12 is chosen as the initial guess, one can stop as