642639 has 4 divisors (see below), whose sum is σ = 856856. Its totient is φ = 428424.

The previous prime is 642623. The next prime is 642673. The reversal of 642639 is 936246.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 642639 - 2⁴ = 642623 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 (642739) 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, 107104 + ... + 107109.

It is an arithmetic number, because the mean of its divisors is an integer number (214214).

2⁶⁴²⁶³⁹ is an apocalyptic number.

642639 is a deficient number, since it is larger than the sum of its proper divisors (214217).

642639 is a wasteful number, since it uses less digits than its factorization.

642639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214216.

The product of its digits is 7776, while the sum is 30.

The square root of 642639 is about 801.6476782228. The cubic root of 642639 is about 86.2956741914.

The spelling of 642639 in words is "six hundred forty-two thousand, six hundred thirty-nine".