643685765 has 4 divisors (see below), whose sum is σ = 772422924. Its totient is φ = 514948608.

The previous prime is 643685761. The next prime is 643685813. The reversal of 643685765 is 567586346.

643685765 is nontrivially palindromic in base 7.

643685765 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 274200481 + 369485284 = 16559^2 + 19222^2 .

It is a cyclic number.

It is not a de Polignac number, because 643685765 - 2² = 643685761 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643685761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64368572 + ... + 64368581.

It is an arithmetic number, because the mean of its divisors is an integer number (193105731).

Almost surely, 2^643685765 is an apocalyptic number.

It is an amenable number.

643685765 is a deficient number, since it is larger than the sum of its proper divisors (128737159).

643685765 is a wasteful number, since it uses less digits than its factorization.

643685765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128737158.

The product of its digits is 3628800, while the sum is 50.

The square root of 643685765 is about 25370.9630286278. The cubic root of 643685765 is about 863.4250312139.

The spelling of 643685765 in words is "six hundred forty-three million, six hundred eighty-five thousand, seven hundred sixty-five".