644920 has 32 divisors (see below), whose sum is σ = 1516320. Its totient is φ = 246400.

The previous prime is 644911. The next prime is 644923. The reversal of 644920 is 29446.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 570 + ... + 1270.

It is an arithmetic number, because the mean of its divisors is an integer number (47385).

2⁶⁴⁴⁹²⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (758160).

644920 is an abundant number, since it is smaller than the sum of its proper divisors (871400).

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

644920 is a wasteful number, since it uses less digits than its factorization.

644920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 735 (or 731 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 644920 is about 803.0691128415. The cubic root of 644920 is about 86.3976536857.

The spelling of 644920 in words is "six hundred forty-four thousand, nine hundred twenty".