644991831 has 36 divisors (see below), whose sum is σ = 1031659720. Its totient is φ = 388000800.

The previous prime is 644991817. The next prime is 644991833. The reversal of 644991831 is 138199446.

It is not a de Polignac number, because 644991831 - 2¹³ = 644983639 is a prime.

It is a super-2 number, since 2×644991831² = 832028924113465122, 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 (644991833) 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 35 ways as a sum of consecutive naturals, for example, 149241 + ... + 153501.

Almost surely, 2^644991831 is an apocalyptic number.

644991831 is a deficient number, since it is larger than the sum of its proper divisors (386667889).

644991831 is a wasteful number, since it uses less digits than its factorization.

644991831 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4428 (or 4414 counting only the distinct ones).

The product of its digits is 186624, while the sum is 45.

The square root of 644991831 is about 25396.6893708609. The cubic root of 644991831 is about 864.0086121505.

The spelling of 644991831 in words is "six hundred forty-four million, nine hundred ninety-one thousand, eight hundred thirty-one".