644865 has 16 divisors (see below), whose sum is σ = 1111488. Its totient is φ = 317376.

The previous prime is 644863. The next prime is 644867. The reversal of 644865 is 568446.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (644863) and next prime (644867).

It is not a de Polignac number, because 644865 - 2¹ = 644863 is a prime.

It is a Curzon number.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (644863) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1459 + ... + 1848.

It is an arithmetic number, because the mean of its divisors is an integer number (69468).

2⁶⁴⁴⁸⁶⁵ is an apocalyptic number.

644865 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

644865 is a deficient number, since it is larger than the sum of its proper divisors (466623).

644865 is a wasteful number, since it uses less digits than its factorization.

644865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3328.

The product of its digits is 23040, while the sum is 33.

The square root of 644865 is about 803.0348684833. The cubic root of 644865 is about 86.3951975640.

The spelling of 644865 in words is "six hundred forty-four thousand, eight hundred sixty-five".