640865 has 4 divisors (see below), whose sum is σ = 769044. Its totient is φ = 512688.

The previous prime is 640859. The next prime is 640873. The reversal of 640865 is 568046.

640865 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 568046 = 2 ⋅284023.

It can be written as a sum of positive squares in 2 ways, for example, as 508369 + 132496 = 713^2 + 364^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640865 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64082 + ... + 64091.

It is an arithmetic number, because the mean of its divisors is an integer number (192261).

2⁶⁴⁰⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

640865 is a deficient number, since it is larger than the sum of its proper divisors (128179).

640865 is a wasteful number, since it uses less digits than its factorization.

640865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128178.

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

The square root of 640865 is about 800.5404424512. The cubic root of 640865 is about 86.2161948315.

The spelling of 640865 in words is "six hundred forty thousand, eight hundred sixty-five".