644978880 has 672 divisors, whose sum is σ = 2875751424. Its totient is φ = 128950272.

The previous prime is 644978869. The next prime is 644978881. The reversal of 644978880 is 88879446.

It is a tau number, because it is divible by the number of its divisors (672).

It is not an unprimeable number, because it can be changed into a prime (644978881) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 6027787 + ... + 6027893.

It is an arithmetic number, because the mean of its divisors is an integer number (4279392).

Almost surely, 2^644978880 is an apocalyptic number.

644978880 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 644978880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1437875712).

644978880 is an abundant number, since it is smaller than the sum of its proper divisors (2230772544).

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

644978880 is a wasteful number, since it uses less digits than its factorization.

644978880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 173 (or 160 counting only the distinct ones).

The product of its (nonzero) digits is 3096576, while the sum is 54.

The square root of 644978880 is about 25396.4343954028. The cubic root of 644978880 is about 864.0028292088.

The spelling of 644978880 in words is "six hundred forty-four million, nine hundred seventy-eight thousand, eight hundred eighty".