644891990 has 8 divisors (see below), whose sum is σ = 1160805600. Its totient is φ = 257956792.

The previous prime is 644891971. The next prime is 644891999. The reversal of 644891990 is 99198446.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644891999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32244590 + ... + 32244609.

It is an arithmetic number, because the mean of its divisors is an integer number (145100700).

Almost surely, 2^644891990 is an apocalyptic number.

644891990 is a deficient number, since it is larger than the sum of its proper divisors (515913610).

644891990 is a wasteful number, since it uses less digits than its factorization.

644891990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64489206.

The product of its (nonzero) digits is 559872, while the sum is 50.

The square root of 644891990 is about 25394.7236645725. The cubic root of 644891990 is about 863.9640286736.

The spelling of 644891990 in words is "six hundred forty-four million, eight hundred ninety-one thousand, nine hundred ninety".