644705 has 4 divisors (see below), whose sum is σ = 773652. Its totient is φ = 515760.

The previous prime is 644701. The next prime is 644717. The reversal of 644705 is 507446.

644705 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in 2 ways, for example, as 430336 + 214369 = 656^2 + 463^2 .

It is not a de Polignac number, because 644705 - 2² = 644701 is a prime.

It is a super-3 number, since 3×644705³ = 803904333728107875, which contains 333 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (644701) 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, 64466 + ... + 64475.

It is an arithmetic number, because the mean of its divisors is an integer number (193413).

2⁶⁴⁴⁷⁰⁵ is an apocalyptic number.

It is an amenable number.

644705 is a deficient number, since it is larger than the sum of its proper divisors (128947).

644705 is a wasteful number, since it uses less digits than its factorization.

644705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128946.

The product of its (nonzero) digits is 3360, while the sum is 26.

The square root of 644705 is about 802.9352402280. The cubic root of 644705 is about 86.3880516885.

The spelling of 644705 in words is "six hundred forty-four thousand, seven hundred five".