644851 has 8 divisors (see below), whose sum is σ = 686880. Its totient is φ = 605176.

The previous prime is 644843. The next prime is 644857. The reversal of 644851 is 158446.

It is not a de Polignac number, because 644851 - 2³ = 644843 is a prime.

644851 is a modest number, since divided by 851 gives 644 as remainder.

It is not an unprimeable number, because it can be changed into a prime (644857) 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 7 ways as a sum of consecutive naturals, for example, 12141 + ... + 12193.

It is an arithmetic number, because the mean of its divisors is an integer number (85860).

2⁶⁴⁴⁸⁵¹ is an apocalyptic number.

644851 is a deficient number, since it is larger than the sum of its proper divisors (42029).

644851 is an frugal number, since it uses more digits than its factorization.

644851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 122 (or 76 counting only the distinct ones).

The product of its digits is 3840, while the sum is 28.

The square root of 644851 is about 803.0261515044. The cubic root of 644851 is about 86.3945723471.

The spelling of 644851 in words is "six hundred forty-four thousand, eight hundred fifty-one".