643986 has 48 divisors (see below), whose sum is σ = 1684800. Its totient is φ = 173664.

The previous prime is 643969. The next prime is 643991. The reversal of 643986 is 689346.

643986 is a `hidden beast` number, since 643 + 9 + 8 + 6 = 666.

643986 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 643986.

It is a congruent number.

It is an unprimeable number.

643986 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 23 ways as a sum of consecutive naturals, for example, 2260 + ... + 2528.

It is an arithmetic number, because the mean of its divisors is an integer number (35100).

2⁶⁴³⁹⁸⁶ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 643986, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (842400).

643986 is an abundant number, since it is smaller than the sum of its proper divisors (1040814).

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

643986 is a wasteful number, since it uses less digits than its factorization.

643986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 303 (or 300 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 643986 is about 802.4873830784. The cubic root of 643986 is about 86.3559253083.

The spelling of 643986 in words is "six hundred forty-three thousand, nine hundred eighty-six".