644643531 has 24 divisors (see below), whose sum is σ = 1066500864. Its totient is φ = 367562160.

The previous prime is 644643479. The next prime is 644643557. The reversal of 644643531 is 135346446.

644643531 is a `hidden beast` number, since 6 + 4 + 4 + 643 + 5 + 3 + 1 = 666.

It is not a de Polignac number, because 644643531 - 2¹⁹ = 644119243 is a prime.

It is a super-2 number, since 2×644643531² = 831130564120295922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644643031) 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 23 ways as a sum of consecutive naturals, for example, 18466 + ... + 40376.

It is an arithmetic number, because the mean of its divisors is an integer number (44437536).

Almost surely, 2^644643531 is an apocalyptic number.

644643531 is a deficient number, since it is larger than the sum of its proper divisors (421857333).

644643531 is a wasteful number, since it uses less digits than its factorization.

644643531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22391 (or 22388 counting only the distinct ones).

The product of its digits is 103680, while the sum is 36.

The square root of 644643531 is about 25389.8312519008. The cubic root of 644643531 is about 863.8530606276.

Adding to 644643531 its reverse (135346446), we get a palindrome (779989977).

The spelling of 644643531 in words is "six hundred forty-four million, six hundred forty-three thousand, five hundred thirty-one".