643788689 has 4 divisors (see below), whose sum is σ = 643850724. Its totient is φ = 643726656.

The previous prime is 643788637. The next prime is 643788697. The reversal of 643788689 is 986887346.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 986887346 = 2 ⋅493443673.

It can be written as a sum of positive squares in 2 ways, for example, as 573363025 + 70425664 = 23945^2 + 8392^2 .

It is a cyclic number.

It is not a de Polignac number, because 643788689 - 2⁸ = 643788433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643781689) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11252 + ... + 37605.

It is an arithmetic number, because the mean of its divisors is an integer number (160962681).

Almost surely, 2^643788689 is an apocalyptic number.

It is an amenable number.

643788689 is a deficient number, since it is larger than the sum of its proper divisors (62035).

643788689 is a wasteful number, since it uses less digits than its factorization.

643788689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62034.

The product of its digits is 13934592, while the sum is 59.

The square root of 643788689 is about 25372.9913293644. The cubic root of 643788689 is about 863.4710487101.

The spelling of 643788689 in words is "six hundred forty-three million, seven hundred eighty-eight thousand, six hundred eighty-nine".