644065 has 4 divisors (see below), whose sum is σ = 772884. Its totient is φ = 515248.

The previous prime is 644057. The next prime is 644089. The reversal of 644065 is 560446.

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: 560446 = 2 ⋅280223.

It can be written as a sum of positive squares in 2 ways, for example, as 108241 + 535824 = 329^2 + 732^2 .

It is a cyclic number.

It is not a de Polignac number, because 644065 - 2³ = 644057 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64402 + ... + 64411.

It is an arithmetic number, because the mean of its divisors is an integer number (193221).

2⁶⁴⁴⁰⁶⁵ is an apocalyptic number.

It is an amenable number.

644065 is a deficient number, since it is larger than the sum of its proper divisors (128819).

644065 is a wasteful number, since it uses less digits than its factorization.

644065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128818.

The product of its (nonzero) digits is 2880, while the sum is 25.

The square root of 644065 is about 802.5366035266. The cubic root of 644065 is about 86.3594563578.

The spelling of 644065 in words is "six hundred forty-four thousand, sixty-five".