643905866 has 16 divisors (see below), whose sum is σ = 986174784. Its totient is φ = 315249984.

The previous prime is 643905863. The next prime is 643905947. The reversal of 643905866 is 668509346.

It is a super-2 number, since 2×643905866² = 829229528538419912, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 643905866.

It is not an unprimeable number, because it can be changed into a prime (643905863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1595 + ... + 35921.

It is an arithmetic number, because the mean of its divisors is an integer number (61635924).

Almost surely, 2^643905866 is an apocalyptic number.

643905866 is a deficient number, since it is larger than the sum of its proper divisors (342268918).

643905866 is a wasteful number, since it uses less digits than its factorization.

643905866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34525.

The product of its (nonzero) digits is 933120, while the sum is 47.

The square root of 643905866 is about 25375.3003134938. The cubic root of 643905866 is about 863.5234327769.

The spelling of 643905866 in words is "six hundred forty-three million, nine hundred five thousand, eight hundred sixty-six".