640928 has 12 divisors (see below), whose sum is σ = 1261890. Its totient is φ = 320448.

The previous prime is 640919. The next prime is 640933. The reversal of 640928 is 829046.

It can be written as a sum of positive squares in only one way, i.e., 595984 + 44944 = 772^2 + 212^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 640928.

It is an unprimeable number.

640928 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9983 + ... + 10046.

2⁶⁴⁰⁹²⁸ is an apocalyptic number.

It is an amenable number.

640928 is a deficient number, since it is larger than the sum of its proper divisors (620962).

640928 is a wasteful number, since it uses less digits than its factorization.

640928 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20039 (or 20031 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 640928 is about 800.5797899023. The cubic root of 640928 is about 86.2190198895.

The spelling of 640928 in words is "six hundred forty thousand, nine hundred twenty-eight".