643865 has 8 divisors (see below), whose sum is σ = 779328. Its totient is φ = 510640.

The previous prime is 643859. The next prime is 643873. The reversal of 643865 is 568346.

643865 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 643865 - 2⁴ = 643849 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 164 + ... + 1146.

It is an arithmetic number, because the mean of its divisors is an integer number (97416).

2⁶⁴³⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

643865 is a deficient number, since it is larger than the sum of its proper divisors (135463).

643865 is a wasteful number, since it uses less digits than its factorization.

643865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1119.

The product of its digits is 17280, while the sum is 32.

The square root of 643865 is about 802.4119889433. The cubic root of 643865 is about 86.3505164322.

The spelling of 643865 in words is "six hundred forty-three thousand, eight hundred sixty-five".