643918817 has 12 divisors (see below), whose sum is σ = 666594240. Its totient is φ = 621947040.

The previous prime is 643918811. The next prime is 643918853. The reversal of 643918817 is 718819346.

643918817 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 643918817 - 2⁴ = 643918801 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643918811) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 171284 + ... + 175002.

It is an arithmetic number, because the mean of its divisors is an integer number (55549520).

Almost surely, 2^643918817 is an apocalyptic number.

It is an amenable number.

643918817 is a deficient number, since it is larger than the sum of its proper divisors (22675423).

643918817 is a wasteful number, since it uses less digits than its factorization.

643918817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3904 (or 3863 counting only the distinct ones).

The product of its digits is 290304, while the sum is 47.

The square root of 643918817 is about 25375.5555013087. Note that the first 4 decimals coincide. The cubic root of 643918817 is about 863.5292221413.

The spelling of 643918817 in words is "six hundred forty-three million, nine hundred eighteen thousand, eight hundred seventeen".