643856918 has 16 divisors (see below), whose sum is σ = 1001134080. Its totient is φ = 310233000.

The previous prime is 643856893. The next prime is 643856953. The reversal of 643856918 is 819658346.

It is a congruent number.

It is an unprimeable number.

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, 6908 + ... + 36543.

It is an arithmetic number, because the mean of its divisors is an integer number (62570880).

Almost surely, 2^643856918 is an apocalyptic number.

643856918 is a deficient number, since it is larger than the sum of its proper divisors (357277162).

643856918 is a wasteful number, since it uses less digits than its factorization.

643856918 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43723.

The product of its digits is 1244160, while the sum is 50.

The square root of 643856918 is about 25374.3358139676. The cubic root of 643856918 is about 863.5015513093.

The spelling of 643856918 in words is "six hundred forty-three million, eight hundred fifty-six thousand, nine hundred eighteen".