644851869 has 4 divisors (see below), whose sum is σ = 859802496. Its totient is φ = 429901244.

The previous prime is 644851847. The next prime is 644851931. The reversal of 644851869 is 968158446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644851869 - 2⁷ = 644851741 is a prime.

It is a super-2 number, since 2×644851869² = 831667865905586322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644852869) 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, 107475309 + ... + 107475314.

It is an arithmetic number, because the mean of its divisors is an integer number (214950624).

Almost surely, 2^644851869 is an apocalyptic number.

It is an amenable number.

644851869 is a deficient number, since it is larger than the sum of its proper divisors (214950627).

644851869 is a wasteful number, since it uses less digits than its factorization.

644851869 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214950626.

The product of its digits is 1658880, while the sum is 51.

The square root of 644851869 is about 25393.9337047256. The cubic root of 644851869 is about 863.9461115546.

The spelling of 644851869 in words is "six hundred forty-four million, eight hundred fifty-one thousand, eight hundred sixty-nine".