644631531 has 4 divisors (see below), whose sum is σ = 859508712. Its totient is φ = 429754352.

The previous prime is 644631521. The next prime is 644631569. The reversal of 644631531 is 135136446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 644631531 - 2⁶ = 644631467 is a prime.

It is a super-2 number, since 2×644631531² = 831099621518807922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 644631492 and 644631501.

It is not an unprimeable number, because it can be changed into a prime (644631521) 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, 107438586 + ... + 107438591.

It is an arithmetic number, because the mean of its divisors is an integer number (214877178).

Almost surely, 2^644631531 is an apocalyptic number.

644631531 is a deficient number, since it is larger than the sum of its proper divisors (214877181).

644631531 is a wasteful number, since it uses less digits than its factorization.

644631531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214877180.

The product of its digits is 25920, while the sum is 33.

The square root of 644631531 is about 25389.5949357212. The cubic root of 644631531 is about 863.8477004037.

Adding to 644631531 its reverse (135136446), we get a palindrome (779767977).

The spelling of 644631531 in words is "six hundred forty-four million, six hundred thirty-one thousand, five hundred thirty-one".