644942605 has 4 divisors (see below), whose sum is σ = 773931132. Its totient is φ = 515954080.

The previous prime is 644942591. The next prime is 644942611. The reversal of 644942605 is 506249446.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 506249446 = 2 ⋅253124723.

It can be written as a sum of positive squares in 2 ways, for example, as 258662889 + 386279716 = 16083^2 + 19654^2 .

It is not a de Polignac number, because 644942605 - 2⁹ = 644942093 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 64494256 + ... + 64494265.

It is an arithmetic number, because the mean of its divisors is an integer number (193482783).

Almost surely, 2^644942605 is an apocalyptic number.

It is an amenable number.

644942605 is a deficient number, since it is larger than the sum of its proper divisors (128988527).

644942605 is a wasteful number, since it uses less digits than its factorization.

644942605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128988526.

The product of its (nonzero) digits is 207360, while the sum is 40.

The square root of 644942605 is about 25395.7202103032. The cubic root of 644942605 is about 863.9866311124.

The spelling of 644942605 in words is "six hundred forty-four million, nine hundred forty-two thousand, six hundred five".