643529665 has 4 divisors (see below), whose sum is σ = 772235604. Its totient is φ = 514823728.

The previous prime is 643529629. The next prime is 643529693. The reversal of 643529665 is 566925346.

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 82029249 + 561500416 = 9057^2 + 23696^2 .

It is a cyclic number.

It is not a de Polignac number, because 643529665 - 2¹¹ = 643527617 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 64352962 + ... + 64352971.

It is an arithmetic number, because the mean of its divisors is an integer number (193058901).

Almost surely, 2^643529665 is an apocalyptic number.

It is an amenable number.

643529665 is a deficient number, since it is larger than the sum of its proper divisors (128705939).

643529665 is a wasteful number, since it uses less digits than its factorization.

643529665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128705938.

The product of its digits is 1166400, while the sum is 46.

The square root of 643529665 is about 25367.8864906007. The cubic root of 643529665 is about 863.3552292746.

It can be divided in two parts, 6435 and 29665, that added together give a square (36100 = 190²).

The spelling of 643529665 in words is "six hundred forty-three million, five hundred twenty-nine thousand, six hundred sixty-five".