643989 has 4 divisors (see below), whose sum is σ = 858656. Its totient is φ = 429324.

The previous prime is 643969. The next prime is 643991. The reversal of 643989 is 989346.

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 not a de Polignac number, because 643989 - 2⁵ = 643957 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643919) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107329 + ... + 107334.

It is an arithmetic number, because the mean of its divisors is an integer number (214664).

2⁶⁴³⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

643989 is a deficient number, since it is larger than the sum of its proper divisors (214667).

643989 is a wasteful number, since it uses less digits than its factorization.

643989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214666.

The product of its digits is 46656, while the sum is 39.

The square root of 643989 is about 802.4892522645. The cubic root of 643989 is about 86.3560594041.

The spelling of 643989 in words is "six hundred forty-three thousand, nine hundred eighty-nine".