643942665 has 24 divisors (see below), whose sum is σ = 1131893568. Its totient is φ = 338597280.

The previous prime is 643942619. The next prime is 643942669. The reversal of 643942665 is 566249346.

It is not a de Polignac number, because 643942665 - 2¹¹ = 643940617 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 643942665.

It is not an unprimeable number, because it can be changed into a prime (643942669) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 97579 + ... + 103968.

It is an arithmetic number, because the mean of its divisors is an integer number (47162232).

Almost surely, 2^643942665 is an apocalyptic number.

It is an amenable number.

643942665 is a deficient number, since it is larger than the sum of its proper divisors (487950903).

643942665 is a wasteful number, since it uses less digits than its factorization.

643942665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201629 (or 201626 counting only the distinct ones).

The product of its digits is 933120, while the sum is 45.

The square root of 643942665 is about 25376.0253980012. The cubic root of 643942665 is about 863.5398824865.

The spelling of 643942665 in words is "six hundred forty-three million, nine hundred forty-two thousand, six hundred sixty-five".