644405 has 6 divisors (see below), whose sum is σ = 775446. Its totient is φ = 514088.

The previous prime is 644401. The next prime is 644411. The reversal of 644405 is 504446.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 515524 + 128881 = 718^2 + 359^2 .

It is not a de Polignac number, because 644405 - 2² = 644401 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644401) by changing a digit.

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 5 ways as a sum of consecutive naturals, for example, 1616 + ... + 1974.

It is an arithmetic number, because the mean of its divisors is an integer number (129241).

2⁶⁴⁴⁴⁰⁵ is an apocalyptic number.

It is an amenable number.

644405 is a deficient number, since it is larger than the sum of its proper divisors (131041).

644405 is an frugal number, since it uses more digits than its factorization.

644405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 723 (or 364 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 23.

The square root of 644405 is about 802.7484039224. The cubic root of 644405 is about 86.3746499847.

The spelling of 644405 in words is "six hundred forty-four thousand, four hundred five".