644083840 has 64 divisors (see below), whose sum is σ = 1559376000. Its totient is φ = 254352384.

The previous prime is 644083837. The next prime is 644083849. The reversal of 644083840 is 48380446.

It is a tau number, because it is divible by the number of its divisors (64).

It is a self number, because there is not a number n which added to its sum of digits gives 644083840.

It is not an unprimeable number, because it can be changed into a prime (644083849) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44191 + ... + 56929.

It is an arithmetic number, because the mean of its divisors is an integer number (24365250).

Almost surely, 2^644083840 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 644083840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (779688000).

644083840 is an abundant number, since it is smaller than the sum of its proper divisors (915292160).

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

644083840 is a wasteful number, since it uses less digits than its factorization.

644083840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12837 (or 12825 counting only the distinct ones).

The product of its (nonzero) digits is 73728, while the sum is 37.

The square root of 644083840 is about 25378.8069065510. The cubic root of 644083840 is about 863.6029840335.

The spelling of 644083840 in words is "six hundred forty-four million, eighty-three thousand, eight hundred forty".