644667760 has 80 divisors (see below), whose sum is σ = 1639180800. Its totient is φ = 233841920.

The previous prime is 644667757. The next prime is 644667763. The reversal of 644667760 is 67766446.

644667760 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (644667757) and next prime (644667763).

It is a tau number, because it is divible by the number of its divisors (80).

It is a Smith number, since the sum of its digits (46) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 644667760.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644667763) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 526509 + ... + 527731.

It is an arithmetic number, because the mean of its divisors is an integer number (20489760).

Almost surely, 2^644667760 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 644667760, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (819590400).

644667760 is an abundant number, since it is smaller than the sum of its proper divisors (994513040).

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

644667760 is a wasteful number, since it uses less digits than its factorization.

644667760 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1846 (or 1840 counting only the distinct ones).

The product of its (nonzero) digits is 1016064, while the sum is 46.

The square root of 644667760 is about 25390.3083872567. The cubic root of 644667760 is about 863.8638831637.

The spelling of 644667760 in words is "six hundred forty-four million, six hundred sixty-seven thousand, seven hundred sixty".