644855 has 4 divisors (see below), whose sum is σ = 773832. Its totient is φ = 515880.

The previous prime is 644843. The next prime is 644857. The reversal of 644855 is 558446.

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

It is not a de Polignac number, because 644855 - 2⁸ = 644599 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644857) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64481 + ... + 64490.

It is an arithmetic number, because the mean of its divisors is an integer number (193458).

2⁶⁴⁴⁸⁵⁵ is an apocalyptic number.

644855 is a deficient number, since it is larger than the sum of its proper divisors (128977).

644855 is a wasteful number, since it uses less digits than its factorization.

644855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128976.

The product of its digits is 19200, while the sum is 32.

The square root of 644855 is about 803.0286420795. The cubic root of 644855 is about 86.3947509814.

The spelling of 644855 in words is "six hundred forty-four thousand, eight hundred fifty-five".