644918 has 4 divisors (see below), whose sum is σ = 967380. Its totient is φ = 322458.

The previous prime is 644911. The next prime is 644923. The reversal of 644918 is 819446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 819446 = 2 ⋅409723.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644918.

It is not an unprimeable number, because it can be changed into a prime (644911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161228 + ... + 161231.

It is an arithmetic number, because the mean of its divisors is an integer number (241845).

2⁶⁴⁴⁹¹⁸ is an apocalyptic number.

644918 is a deficient number, since it is larger than the sum of its proper divisors (322462).

644918 is a wasteful number, since it uses less digits than its factorization.

644918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322461.

The product of its digits is 6912, while the sum is 32.

The square root of 644918 is about 803.0678676177. The cubic root of 644918 is about 86.3975643746.

The spelling of 644918 in words is "six hundred forty-four thousand, nine hundred eighteen".