640856 has 8 divisors (see below), whose sum is σ = 1201620. Its totient is φ = 320424.

The previous prime is 640853. The next prime is 640859. The reversal of 640856 is 658046.

640856 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (640853) and next prime (640859).

It is a tau number, because it is divible by the number of its divisors (8).

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640856.

It is not an unprimeable number, because it can be changed into a prime (640853) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40046 + ... + 40061.

2⁶⁴⁰⁸⁵⁶ is an apocalyptic number.

It is an amenable number.

640856 is a deficient number, since it is larger than the sum of its proper divisors (560764).

640856 is a wasteful number, since it uses less digits than its factorization.

640856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80113 (or 80109 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 640856 is about 800.5348212289. The cubic root of 640856 is about 86.2157912367.

The spelling of 640856 in words is "six hundred forty thousand, eight hundred fifty-six".