640556 has 12 divisors (see below), whose sum is σ = 1281168. Its totient is φ = 274512.

The previous prime is 640531. The next prime is 640579. The reversal of 640556 is 655046.

640556 is an admirable number.

It is an unprimeable number.

640556 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 in 3 ways as a sum of consecutive naturals, for example, 11411 + ... + 11466.

It is an arithmetic number, because the mean of its divisors is an integer number (106764).

2⁶⁴⁰⁵⁵⁶ is an apocalyptic number.

It is an amenable number.

640556 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

640556 is a wasteful number, since it uses less digits than its factorization.

640556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22888 (or 22886 counting only the distinct ones).

The product of its (nonzero) digits is 3600, while the sum is 26.

The square root of 640556 is about 800.3474245601. The cubic root of 640556 is about 86.2023359132.

The spelling of 640556 in words is "six hundred forty thousand, five hundred fifty-six".