643939 has 4 divisors (see below), whose sum is σ = 645624. Its totient is φ = 642256.

The previous prime is 643927. The next prime is 643949. The reversal of 643939 is 939346.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 939346 = 2 ⋅469673.

It is a cyclic number.

It is not a de Polignac number, because 643939 - 2¹¹ = 641891 is a prime.

It is a Duffinian number.

643939 is a lucky 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, 39 + ... + 1135.

It is an arithmetic number, because the mean of its divisors is an integer number (161406).

2⁶⁴³⁹³⁹ is an apocalyptic number.

643939 is a deficient number, since it is larger than the sum of its proper divisors (1685).

643939 is a wasteful number, since it uses less digits than its factorization.

643939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1684.

The product of its digits is 17496, while the sum is 34.

The square root of 643939 is about 802.4580985946. The cubic root of 643939 is about 86.3538244204.

The spelling of 643939 in words is "six hundred forty-three thousand, nine hundred thirty-nine".