644992 has 16 divisors (see below), whose sum is σ = 1285200. Its totient is φ = 322432.

The previous prime is 644977. The next prime is 644999. The reversal of 644992 is 299446.

It is a tau number, because it is divible by the number of its divisors (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644999) by changing a digit.

644992 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 as a sum of consecutive naturals, namely, 2392 + ... + 2647.

It is an arithmetic number, because the mean of its divisors is an integer number (80325).

2⁶⁴⁴⁹⁹² is an apocalyptic number.

It is an amenable number.

644992 is a deficient number, since it is larger than the sum of its proper divisors (640208).

644992 is an equidigital number, since it uses as much as digits as its factorization.

644992 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5053 (or 5041 counting only the distinct ones).

The product of its digits is 15552, while the sum is 34.

The square root of 644992 is about 803.1139396126. The cubic root of 644992 is about 86.4008687613.

The spelling of 644992 in words is "six hundred forty-four thousand, nine hundred ninety-two".