646639 has 4 divisors (see below), whose sum is σ = 739024. Its totient is φ = 554256.

The previous prime is 646637. The next prime is 646643. The reversal of 646639 is 936646.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 936646 = 2 ⋅468323.

It is a cyclic number.

It is not a de Polignac number, because 646639 - 2¹ = 646637 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46182 + ... + 46195.

It is an arithmetic number, because the mean of its divisors is an integer number (184756).

2⁶⁴⁶⁶³⁹ is an apocalyptic number.

646639 is a deficient number, since it is larger than the sum of its proper divisors (92385).

646639 is an equidigital number, since it uses as much as digits as its factorization.

646639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92384.

The product of its digits is 23328, while the sum is 34.

The square root of 646639 is about 804.1386696335. The cubic root of 646639 is about 86.4743483696.

The spelling of 646639 in words is "six hundred forty-six thousand, six hundred thirty-nine".