643997764 has 12 divisors (see below), whose sum is σ = 1127459088. Its totient is φ = 321866600.

The previous prime is 643997759. The next prime is 643997789. The reversal of 643997764 is 467799346.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21682 + ... + 41929.

It is an arithmetic number, because the mean of its divisors is an integer number (93954924).

Almost surely, 2^643997764 is an apocalyptic number.

It is an amenable number.

643997764 is a deficient number, since it is larger than the sum of its proper divisors (483461324).

643997764 is a wasteful number, since it uses less digits than its factorization.

643997764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66146 (or 66144 counting only the distinct ones).

The product of its digits is 6858432, while the sum is 55.

The square root of 643997764 is about 25377.1110254891. Note that the first 3 decimals coincide. The cubic root of 643997764 is about 863.5645114012.

The spelling of 643997764 in words is "six hundred forty-three million, nine hundred ninety-seven thousand, seven hundred sixty-four".