644811905 has 4 divisors (see below), whose sum is σ = 773774292. Its totient is φ = 515849520.

The previous prime is 644811901. The next prime is 644811917. The reversal of 644811905 is 509118446.

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 469328896 + 175483009 = 21664^2 + 13247^2 .

It is not a de Polignac number, because 644811905 - 2² = 644811901 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644811901) 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, 64481186 + ... + 64481195.

It is an arithmetic number, because the mean of its divisors is an integer number (193443573).

Almost surely, 2^644811905 is an apocalyptic number.

It is an amenable number.

644811905 is a deficient number, since it is larger than the sum of its proper divisors (128962387).

644811905 is a wasteful number, since it uses less digits than its factorization.

644811905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128962386.

The product of its (nonzero) digits is 34560, while the sum is 38.

The square root of 644811905 is about 25393.1468116892. The cubic root of 644811905 is about 863.9282638093.

The spelling of 644811905 in words is "six hundred forty-four million, eight hundred eleven thousand, nine hundred five".