644139240 has 64 divisors (see below), whose sum is σ = 1938375360. Its totient is φ = 171240960.

The previous prime is 644139239. The next prime is 644139241. The reversal of 644139240 is 42931446.

It is an interprime number because it is at equal distance from previous prime (644139239) and next prime (644139241).

It is not an unprimeable number, because it can be changed into a prime (644139241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 31612 + ... + 47828.

It is an arithmetic number, because the mean of its divisors is an integer number (30287115).

Almost surely, 2^644139240 is an apocalyptic number.

644139240 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 644139240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (969187680).

644139240 is an abundant number, since it is smaller than the sum of its proper divisors (1294236120).

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

644139240 is a wasteful number, since it uses less digits than its factorization.

644139240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16562 (or 16558 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 33.

The square root of 644139240 is about 25379.8983449501. The cubic root of 644139240 is about 863.6277438710.

The spelling of 644139240 in words is "six hundred forty-four million, one hundred thirty-nine thousand, two hundred forty".