644009 has 2 divisors, whose sum is σ = 644010. Its totient is φ = 644008.

The previous prime is 643991. The next prime is 644029. The reversal of 644009 is 900446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 570025 + 73984 = 755^2 + 272^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644009 is a prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644009.

It is not a weakly prime, because it can be changed into another prime (644029) 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 as a sum of consecutive naturals, namely, 322004 + 322005.

It is an arithmetic number, because the mean of its divisors is an integer number (322005).

2⁶⁴⁴⁰⁰⁹ is an apocalyptic number.

It is an amenable number.

644009 is a deficient number, since it is larger than the sum of its proper divisors (1).

644009 is an equidigital number, since it uses as much as digits as its factorization.

644009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 644009 is about 802.5017133938. The cubic root of 644009 is about 86.3569533652.

The spelling of 644009 in words is "six hundred forty-four thousand, nine".