644845 has 4 divisors (see below), whose sum is σ = 773820. Its totient is φ = 515872.

The previous prime is 644843. The next prime is 644857. The reversal of 644845 is 548446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 548446 = 2 ⋅274223.

It can be written as a sum of positive squares in 2 ways, for example, as 227529 + 417316 = 477^2 + 646^2 .

It is a cyclic number.

It is not a de Polignac number, because 644845 - 2¹ = 644843 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644843) 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, 64480 + ... + 64489.

It is an arithmetic number, because the mean of its divisors is an integer number (193455).

2⁶⁴⁴⁸⁴⁵ is an apocalyptic number.

It is an amenable number.

644845 is a deficient number, since it is larger than the sum of its proper divisors (128975).

644845 is a wasteful number, since it uses less digits than its factorization.

644845 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128974.

The product of its digits is 15360, while the sum is 31.

The square root of 644845 is about 803.0224156274. The cubic root of 644845 is about 86.3943043942.

The spelling of 644845 in words is "six hundred forty-four thousand, eight hundred forty-five".