643994 has 32 divisors (see below), whose sum is σ = 1161216. Its totient is φ = 264960.

The previous prime is 643991. The next prime is 644009. The reversal of 643994 is 499346.

It is a happy number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (643991) 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 15 ways as a sum of consecutive naturals, for example, 13679 + ... + 13725.

It is an arithmetic number, because the mean of its divisors is an integer number (36288).

2⁶⁴³⁹⁹⁴ is an apocalyptic number.

643994 is a deficient number, since it is larger than the sum of its proper divisors (517222).

643994 is a wasteful number, since it uses less digits than its factorization.

643994 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110.

The product of its digits is 23328, while the sum is 35.

The square root of 643994 is about 802.4923675650. The cubic root of 643994 is about 86.3562828961.

The spelling of 643994 in words is "six hundred forty-three thousand, nine hundred ninety-four".