644987991 has 8 divisors (see below), whose sum is σ = 860407920. Its totient is φ = 429780032.

The previous prime is 644987983. The next prime is 644987999. The reversal of 644987991 is 199789446.

It is an interprime number because it is at equal distance from previous prime (644987983) and next prime (644987999).

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

It is a cyclic number.

It is not a de Polignac number, because 644987991 - 2³ = 644987983 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644987999) 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 7 ways as a sum of consecutive naturals, for example, 45750 + ... + 58163.

It is an arithmetic number, because the mean of its divisors is an integer number (107550990).

Almost surely, 2^644987991 is an apocalyptic number.

644987991 is a deficient number, since it is larger than the sum of its proper divisors (215419929).

644987991 is a wasteful number, since it uses less digits than its factorization.

644987991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105985.

The product of its digits is 3919104, while the sum is 57.

The square root of 644987991 is about 25396.6137703435. The cubic root of 644987991 is about 864.0068975037.

The spelling of 644987991 in words is "six hundred forty-four million, nine hundred eighty-seven thousand, nine hundred ninety-one".