644189309 has 2 divisors, whose sum is σ = 644189310. Its totient is φ = 644189308.

The previous prime is 644189263. The next prime is 644189353. The reversal of 644189309 is 903981446.

It is an a-pointer prime, because the next prime (644189353) can be obtained adding 644189309 to its sum of digits (44).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 610584100 + 33605209 = 24710^2 + 5797^2 .

It is a cyclic number.

It is not a de Polignac number, because 644189309 - 2²⁰ = 643140733 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644189309.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644179309) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322094654 + 322094655.

It is an arithmetic number, because the mean of its divisors is an integer number (322094655).

Almost surely, 2^644189309 is an apocalyptic number.

It is an amenable number.

644189309 is a deficient number, since it is larger than the sum of its proper divisors (1).

644189309 is an equidigital number, since it uses as much as digits as its factorization.

644189309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 186624, while the sum is 44.

The square root of 644189309 is about 25380.8847166524. The cubic root of 644189309 is about 863.6501199115.

The spelling of 644189309 in words is "six hundred forty-four million, one hundred eighty-nine thousand, three hundred nine".