644257309 has 2 divisors, whose sum is σ = 644257310. Its totient is φ = 644257308.

The previous prime is 644257297. The next prime is 644257321. The reversal of 644257309 is 903752446.

It is a happy number.

644257309 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a balanced prime because it is at equal distance from previous prime (644257297) and next prime (644257321).

It can be written as a sum of positive squares in only one way, i.e., 572262084 + 71995225 = 23922^2 + 8485^2 .

It is a cyclic number.

It is not a de Polignac number, because 644257309 - 2⁵ = 644257277 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644257609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322128654 + 322128655.

It is an arithmetic number, because the mean of its divisors is an integer number (322128655).

Almost surely, 2^644257309 is an apocalyptic number.

It is an amenable number.

644257309 is a deficient number, since it is larger than the sum of its proper divisors (1).

644257309 is an equidigital number, since it uses as much as digits as its factorization.

644257309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 181440, while the sum is 40.

The square root of 644257309 is about 25382.2242721161. The cubic root of 644257309 is about 863.6805075326.

The spelling of 644257309 in words is "six hundred forty-four million, two hundred fifty-seven thousand, three hundred nine".