643728643 has 8 divisors (see below), whose sum is σ = 648410112. Its totient is φ = 639063816.

The previous prime is 643728611. The next prime is 643728649. The reversal of 643728643 is 346827346.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 643728643 - 2⁵ = 643728611 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 643728643.

It is not an unprimeable number, because it can be changed into a prime (643728649) 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, 79446 + ... + 87172.

It is an arithmetic number, because the mean of its divisors is an integer number (81051264).

Almost surely, 2^643728643 is an apocalyptic number.

643728643 is a deficient number, since it is larger than the sum of its proper divisors (4681469).

643728643 is a wasteful number, since it uses less digits than its factorization.

643728643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8321.

The product of its digits is 580608, while the sum is 43.

The square root of 643728643 is about 25371.8080356919. The cubic root of 643728643 is about 863.4442026370. Note that the first 3 decimals are identical.

The spelling of 643728643 in words is "six hundred forty-three million, seven hundred twenty-eight thousand, six hundred forty-three".