644856867 has 6 divisors (see below), whose sum is σ = 931459932. Its totient is φ = 429904572.

The previous prime is 644856857. The next prime is 644856889. The reversal of 644856867 is 768658446.

It is not a de Polignac number, because 644856867 - 2⁷ = 644856739 is a prime.

It is not an unprimeable number, because it can be changed into a prime (644856857) 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 5 ways as a sum of consecutive naturals, for example, 35825373 + ... + 35825390.

It is an arithmetic number, because the mean of its divisors is an integer number (155243322).

Almost surely, 2^644856867 is an apocalyptic number.

644856867 is a deficient number, since it is larger than the sum of its proper divisors (286603065).

644856867 is a wasteful number, since it uses less digits than its factorization.

644856867 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71650769 (or 71650766 counting only the distinct ones).

The product of its digits is 7741440, while the sum is 54.

The square root of 644856867 is about 25394.0321138649. The cubic root of 644856867 is about 863.9483435873.

The spelling of 644856867 in words is "six hundred forty-four million, eight hundred fifty-six thousand, eight hundred sixty-seven".