640811869 has 4 divisors (see below), whose sum is σ = 662908860. Its totient is φ = 618714880.

The previous prime is 640811851. The next prime is 640811911. The reversal of 640811869 is 968118046.

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 152843769 + 487968100 = 12363^2 + 22090^2 .

It is a cyclic number.

It is not a de Polignac number, because 640811869 - 2⁷ = 640811741 is a prime.

It is a super-2 number, since 2×640811869² = 821279702902546322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640811839) 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 3 ways as a sum of consecutive naturals, for example, 11048452 + ... + 11048509.

It is an arithmetic number, because the mean of its divisors is an integer number (165727215).

Almost surely, 2^640811869 is an apocalyptic number.

It is an amenable number.

640811869 is a deficient number, since it is larger than the sum of its proper divisors (22096991).

640811869 is a wasteful number, since it uses less digits than its factorization.

640811869 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22096990.

The product of its (nonzero) digits is 82944, while the sum is 43.

The square root of 640811869 is about 25314.2621658226. The cubic root of 640811869 is about 862.1381217723.

The spelling of 640811869 in words is "six hundred forty million, eight hundred eleven thousand, eight hundred sixty-nine".