643861 has 4 divisors (see below), whose sum is σ = 647424. Its totient is φ = 640300.

The previous prime is 643859. The next prime is 643873. The reversal of 643861 is 168346.

643861 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 a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 643861 - 2¹ = 643859 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 (643061) 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, 1495 + ... + 1876.

It is an arithmetic number, because the mean of its divisors is an integer number (161856).

2⁶⁴³⁸⁶¹ is an apocalyptic number.

It is an amenable number.

643861 is a deficient number, since it is larger than the sum of its proper divisors (3563).

643861 is a wasteful number, since it uses less digits than its factorization.

643861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3562.

The product of its digits is 3456, while the sum is 28.

The square root of 643861 is about 802.4094964543. The cubic root of 643861 is about 86.3503376148.

The spelling of 643861 in words is "six hundred forty-three thousand, eight hundred sixty-one".