644362640 has 20 divisors (see below), whose sum is σ = 1498143324. Its totient is φ = 257745024.

The previous prime is 644362639. The next prime is 644362661. The reversal of 644362640 is 46263446.

It can be written as a sum of positive squares in 2 ways, for example, as 512388496 + 131974144 = 22636^2 + 11488^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a hoax number, since the sum of its digits (35) coincides with the sum of the digits of its distinct prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 644362640.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4027187 + ... + 4027346.

Almost surely, 2^644362640 is an apocalyptic number.

It is an amenable number.

644362640 is an abundant number, since it is smaller than the sum of its proper divisors (853780684).

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

644362640 is a wasteful number, since it uses less digits than its factorization.

644362640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8054546 (or 8054540 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 35.

The square root of 644362640 is about 25384.2990842765. The cubic root of 644362640 is about 863.7275732898.

It can be divided in two parts, 64436 and 2640, that added together give a palindrome (67076).

The spelling of 644362640 in words is "six hundred forty-four million, three hundred sixty-two thousand, six hundred forty".