644020920 has 96 divisors (see below), whose sum is σ = 2127453120. Its totient is φ = 168917760.

The previous prime is 644020913. The next prime is 644020921. The reversal of 644020920 is 29020446.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644020921) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7297 + ... + 36623.

It is an arithmetic number, because the mean of its divisors is an integer number (22160970).

Almost surely, 2^644020920 is an apocalyptic number.

644020920 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644020920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1063726560).

644020920 is an abundant number, since it is smaller than the sum of its proper divisors (1483432200).

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

644020920 is a wasteful number, since it uses less digits than its factorization.

644020920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29405 (or 29398 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 644020920 is about 25377.5672592942. The cubic root of 644020920 is about 863.5748615718.

The spelling of 644020920 in words is "six hundred forty-four million, twenty thousand, nine hundred twenty".