644640233 has 4 divisors (see below), whose sum is σ = 662062980. Its totient is φ = 627217488.

The previous prime is 644640193. The next prime is 644640247. The reversal of 644640233 is 332046446.

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 218093824 + 426546409 = 14768^2 + 20653^2 .

It is not a de Polignac number, because 644640233 - 2²² = 640445929 is a prime.

It is a super-2 number, since 2×644640233² = 831122060004588578, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 644640233.

It is not an unprimeable number, because it can be changed into a prime (644640533) 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, 8711318 + ... + 8711391.

It is an arithmetic number, because the mean of its divisors is an integer number (165515745).

Almost surely, 2^644640233 is an apocalyptic number.

It is an amenable number.

644640233 is a deficient number, since it is larger than the sum of its proper divisors (17422747).

644640233 is a wasteful number, since it uses less digits than its factorization.

644640233 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17422746.

The product of its (nonzero) digits is 41472, while the sum is 32.

The square root of 644640233 is about 25389.7663045566. The cubic root of 644640233 is about 863.8515874660.

Adding to 644640233 its reverse (332046446), we get a palindrome (976686679).

The spelling of 644640233 in words is "six hundred forty-four million, six hundred forty thousand, two hundred thirty-three".