644008640 has 56 divisors (see below), whose sum is σ = 1672967952. Its totient is φ = 234183680.

The previous prime is 644008609. The next prime is 644008661. The reversal of 644008640 is 46800446.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a junction number, because it is equal to n+sod(n) for n = 644008597 and 644008606.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 87959 + ... + 94998.

Almost surely, 2^644008640 is an apocalyptic number.

It is an amenable number.

644008640 is an abundant number, since it is smaller than the sum of its proper divisors (1028959312).

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

644008640 is a wasteful number, since it uses less digits than its factorization.

644008640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182985 (or 182975 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 32.

The square root of 644008640 is about 25377.3253121758. The cubic root of 644008640 is about 863.5693727405.

The spelling of 644008640 in words is "six hundred forty-four million, eight thousand, six hundred forty".