644139 has 8 divisors (see below), whose sum is σ = 954320. Its totient is φ = 429408.

The previous prime is 644131. The next prime is 644141. The reversal of 644139 is 931446.

644139 is a `hidden beast` number, since 644 + 13 + 9 = 666.

644139 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 644139 - 2³ = 644131 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 23857 = 644139 / (6 + 4 + 4 + 1 + 3 + 9).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644131) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11902 + ... + 11955.

It is an arithmetic number, because the mean of its divisors is an integer number (119290).

2⁶⁴⁴¹³⁹ is an apocalyptic number.

644139 is a deficient number, since it is larger than the sum of its proper divisors (310181).

644139 is a wasteful number, since it uses less digits than its factorization.

644139 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23866 (or 23860 counting only the distinct ones).

The product of its digits is 2592, while the sum is 27.

The square root of 644139 is about 802.5827060185. The cubic root of 644139 is about 86.3627636611.

The spelling of 644139 in words is "six hundred forty-four thousand, one hundred thirty-nine".