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
Zeisel number additionally has prime factors with the relationship described above, so a name like Brown-Zeisel Numbers might be more appropriate. Hardy–Ramanujan's number 1729 is also a Zeisel number. Zeisel number A Zeisel number, named after Helmut Zeisel, is a square-free integer "k" with at least three prime factors which fall into the pattern where "a" and "b" are some integer constants and "x" is the index number of each prime factor in the factorization, sorted from lowest to highest. For the purpose of determining Zeisel numbers, formula_2. The first few Zeisel numbers are To give an example, 1729 is a Zeisel