643871 has 4 divisors (see below), whose sum is σ = 645792. Its totient is φ = 641952.

The previous prime is 643859. The next prime is 643873. The reversal of 643871 is 178346.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643871 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643873) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 311 + ... + 1176.

It is an arithmetic number, because the mean of its divisors is an integer number (161448).

2⁶⁴³⁸⁷¹ is an apocalyptic number.

643871 is a deficient number, since it is larger than the sum of its proper divisors (1921).

643871 is a wasteful number, since it uses less digits than its factorization.

643871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1920.

The product of its digits is 4032, while the sum is 29.

The square root of 643871 is about 802.4157276624. The cubic root of 643871 is about 86.3507846569.

The spelling of 643871 in words is "six hundred forty-three thousand, eight hundred seventy-one".