644216989 has 16 divisors (see below), whose sum is σ = 738361008. Its totient is φ = 556803072.

The previous prime is 644216987. The next prime is 644217011. The reversal of 644216989 is 989612446.

It can be written as a sum of positive squares in 8 ways, for example, as 27092025 + 617124964 = 5205^2 + 24842^2 .

It is a cyclic number.

It is not a de Polignac number, because 644216989 - 2¹ = 644216987 is a prime.

It is a super-2 number, since 2×644216989² = 830031057832452242, 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 (644216981) 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 15 ways as a sum of consecutive naturals, for example, 36139 + ... + 50935.

It is an arithmetic number, because the mean of its divisors is an integer number (46147563).

Almost surely, 2^644216989 is an apocalyptic number.

It is an amenable number.

644216989 is a deficient number, since it is larger than the sum of its proper divisors (94144019).

644216989 is a wasteful number, since it uses less digits than its factorization.

644216989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15024.

The product of its digits is 746496, while the sum is 49.

The square root of 644216989 is about 25381.4300030554. The cubic root of 644216989 is about 863.6624897188.

The spelling of 644216989 in words is "six hundred forty-four million, two hundred sixteen thousand, nine hundred eighty-nine".