644509 has 4 divisors (see below), whose sum is σ = 646204. Its totient is φ = 642816.

The previous prime is 644507. The next prime is 644513. The reversal of 644509 is 905446.

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 363609 + 280900 = 603^2 + 530^2 .

It is a cyclic number.

It is not a de Polignac number, because 644509 - 2¹ = 644507 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 (644507) 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, 19 + ... + 1135.

It is an arithmetic number, because the mean of its divisors is an integer number (161551).

2⁶⁴⁴⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

644509 is a deficient number, since it is larger than the sum of its proper divisors (1695).

644509 is a wasteful number, since it uses less digits than its factorization.

644509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1694.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 644509 is about 802.8131787658. The cubic root of 644509 is about 86.3792963796.

The spelling of 644509 in words is "six hundred forty-four thousand, five hundred nine".