644724720 has 120 divisors (see below), whose sum is σ = 2279206800. Its totient is φ = 162874368.

The previous prime is 644724697. The next prime is 644724733. The reversal of 644724720 is 27427446.

It is a happy number.

644724720 is a `hidden beast` number, since 644 + 7 + 2 + 4 + 7 + 2 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9885 + ... + 37244.

It is an arithmetic number, because the mean of its divisors is an integer number (18993390).

Almost surely, 2^644724720 is an apocalyptic number.

644724720 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 644724720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1139603400).

644724720 is an abundant number, since it is smaller than the sum of its proper divisors (1634482080).

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

644724720 is a wasteful number, since it uses less digits than its factorization.

644724720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47167 (or 47158 counting only the distinct ones).

The product of its (nonzero) digits is 75264, while the sum is 36.

The square root of 644724720 is about 25391.4300503142. The cubic root of 644724720 is about 863.8893248153.

The spelling of 644724720 in words is "six hundred forty-four million, seven hundred twenty-four thousand, seven hundred twenty".