644445021 has 32 divisors (see below), whose sum is σ = 1013414400. Its totient is φ = 360002880.

The previous prime is 644445017. The next prime is 644445041. The reversal of 644445021 is 120544446.

It is a happy number.

It is not a de Polignac number, because 644445021 - 2² = 644445017 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644445021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644445041) 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 31 ways as a sum of consecutive naturals, for example, 9310 + ... + 37088.

It is an arithmetic number, because the mean of its divisors is an integer number (31669200).

Almost surely, 2^644445021 is an apocalyptic number.

It is an amenable number.

644445021 is a deficient number, since it is larger than the sum of its proper divisors (368969379).

644445021 is a wasteful number, since it uses less digits than its factorization.

644445021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27849.

The product of its (nonzero) digits is 15360, while the sum is 30.

The square root of 644445021 is about 25385.9217086952. The cubic root of 644445021 is about 863.7643805701.

Adding to 644445021 its reverse (120544446), we get a palindrome (764989467).

The spelling of 644445021 in words is "six hundred forty-four million, four hundred forty-five thousand, twenty-one".