643864 has 32 divisors (see below), whose sum is σ = 1340640. Its totient is φ = 288000.

The previous prime is 643859. The next prime is 643873. The reversal of 643864 is 468346.

It is a congruent number.

It is an unprimeable number.

643864 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 7 ways as a sum of consecutive naturals, for example, 4189 + ... + 4339.

It is an arithmetic number, because the mean of its divisors is an integer number (41895).

2⁶⁴³⁸⁶⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 643864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (670320).

643864 is an abundant number, since it is smaller than the sum of its proper divisors (696776).

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

643864 is a wasteful number, since it uses less digits than its factorization.

643864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 211 (or 207 counting only the distinct ones).

The product of its digits is 13824, while the sum is 31.

The square root of 643864 is about 802.4113658218. The cubic root of 643864 is about 86.3504717280.

The spelling of 643864 in words is "six hundred forty-three thousand, eight hundred sixty-four".