644909 has 2 divisors, whose sum is σ = 644910. Its totient is φ = 644908.

The previous prime is 644899. The next prime is 644911. The reversal of 644909 is 909446.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 644809 + 100 = 803^2 + 10^2 .

It is a cyclic number.

It is not a de Polignac number, because 644909 - 2⁸ = 644653 is a prime.

Together with 644911, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322454 + 322455.

It is an arithmetic number, because the mean of its divisors is an integer number (322455).

2⁶⁴⁴⁹⁰⁹ is an apocalyptic number.

It is an amenable number.

644909 is a deficient number, since it is larger than the sum of its proper divisors (1).

644909 is an equidigital number, since it uses as much as digits as its factorization.

644909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 32.

The square root of 644909 is about 803.0622640867. The cubic root of 644909 is about 86.3971624725.

The spelling of 644909 in words is "six hundred forty-four thousand, nine hundred nine".