644910881 has 4 divisors (see below), whose sum is σ = 645720852. Its totient is φ = 644100912.

The previous prime is 644910857. The next prime is 644910899. The reversal of 644910881 is 188019446.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 330912481 + 313998400 = 18191^2 + 17720^2 .

It is a cyclic number.

It is not a de Polignac number, because 644910881 - 2¹⁸ = 644648737 is a prime.

It is a super-2 number, since 2×644910881² = 831820088864392322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644910281) 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, 403790 + ... + 405383.

It is an arithmetic number, because the mean of its divisors is an integer number (161430213).

Almost surely, 2^644910881 is an apocalyptic number.

It is an amenable number.

644910881 is a deficient number, since it is larger than the sum of its proper divisors (809971).

644910881 is an equidigital number, since it uses as much as digits as its factorization.

644910881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 809970.

The product of its (nonzero) digits is 55296, while the sum is 41.

The square root of 644910881 is about 25395.0956091919. The cubic root of 644910881 is about 863.9724647039.

The spelling of 644910881 in words is "six hundred forty-four million, nine hundred ten thousand, eight hundred eighty-one".