644120881 has 4 divisors (see below), whose sum is σ = 678022000. Its totient is φ = 610219764.

The previous prime is 644120879. The next prime is 644120887. The reversal of 644120881 is 188021446.

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, and also an emirpimes, since its reverse is a distinct semiprime: 188021446 = 2 ⋅94010723.

It is a cyclic number.

It is not a de Polignac number, because 644120881 - 2¹ = 644120879 is a prime.

It is a super-2 number, since 2×644120881² = 829783418680432322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644120887) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16950531 + ... + 16950568.

It is an arithmetic number, because the mean of its divisors is an integer number (169505500).

Almost surely, 2^644120881 is an apocalyptic number.

It is an amenable number.

644120881 is a deficient number, since it is larger than the sum of its proper divisors (33901119).

644120881 is a wasteful number, since it uses less digits than its factorization.

644120881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33901118.

The product of its (nonzero) digits is 12288, while the sum is 34.

The square root of 644120881 is about 25379.5366584971. The cubic root of 644120881 is about 863.6195388684.

The spelling of 644120881 in words is "six hundred forty-four million, one hundred twenty thousand, eight hundred eighty-one".