644388 has 12 divisors (see below), whose sum is σ = 1503600. Its totient is φ = 214792.

The previous prime is 644383. The next prime is 644401. The reversal of 644388 is 883446.

It is a tau number, because it is divible by the number of its divisors (12).

It is not an unprimeable number, because it can be changed into a prime (644381) by changing a digit.

644388 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26838 + ... + 26861.

It is an arithmetic number, because the mean of its divisors is an integer number (125300).

2⁶⁴⁴³⁸⁸ is an apocalyptic number.

It is an amenable number.

644388 is an abundant number, since it is smaller than the sum of its proper divisors (859212).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644388 is a wasteful number, since it uses less digits than its factorization.

644388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53706 (or 53704 counting only the distinct ones).

The product of its digits is 18432, while the sum is 33.

The square root of 644388 is about 802.7378152299. The cubic root of 644388 is about 86.3738904303.

It can be divided in two parts, 64438 and 8, that added together give a palindrome (64446).

The spelling of 644388 in words is "six hundred forty-four thousand, three hundred eighty-eight".