643686 has 16 divisors (see below), whose sum is σ = 1306368. Its totient is φ = 211400.

The previous prime is 643681. The next prime is 643691. The reversal of 643686 is 686346.

643686 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (643681) and next prime (643691).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643681) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 330 + ... + 1181.

It is an arithmetic number, because the mean of its divisors is an integer number (81648).

2⁶⁴³⁶⁸⁶ is an apocalyptic number.

643686 is an abundant number, since it is smaller than the sum of its proper divisors (662682).

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

643686 is a wasteful number, since it uses less digits than its factorization.

643686 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1587.

The product of its digits is 20736, while the sum is 33.

The square root of 643686 is about 802.3004424778. The cubic root of 643686 is about 86.3425136288.

The spelling of 643686 in words is "six hundred forty-three thousand, six hundred eighty-six".