643917638 has 32 divisors (see below), whose sum is σ = 1251344640. Its totient is φ = 241328160.

The previous prime is 643917613. The next prime is 643917643. The reversal of 643917638 is 836719346.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 643917592 and 643917601.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 89648 + ... + 96563.

It is an arithmetic number, because the mean of its divisors is an integer number (39104520).

Almost surely, 2^643917638 is an apocalyptic number.

643917638 is a deficient number, since it is larger than the sum of its proper divisors (607427002).

643917638 is a wasteful number, since it uses less digits than its factorization.

643917638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186252.

The product of its digits is 653184, while the sum is 47.

The square root of 643917638 is about 25375.5322702796. The cubic root of 643917638 is about 863.5286951072.

The spelling of 643917638 in words is "six hundred forty-three million, nine hundred seventeen thousand, six hundred thirty-eight".