644777789 has 2 divisors, whose sum is σ = 644777790. Its totient is φ = 644777788.

The previous prime is 644777779. The next prime is 644777801. The reversal of 644777789 is 987777446.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 542424100 + 102353689 = 23290^2 + 10117^2 .

It is a cyclic number.

It is not a de Polignac number, because 644777789 - 2⁸ = 644777533 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644777729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322388894 + 322388895.

It is an arithmetic number, because the mean of its divisors is an integer number (322388895).

Almost surely, 2^644777789 is an apocalyptic number.

It is an amenable number.

644777789 is a deficient number, since it is larger than the sum of its proper divisors (1).

644777789 is an equidigital number, since it uses as much as digits as its factorization.

644777789 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16595712, while the sum is 59.

The square root of 644777789 is about 25392.4750467535. The cubic root of 644777789 is about 863.9130271714.

The spelling of 644777789 in words is "six hundred forty-four million, seven hundred seventy-seven thousand, seven hundred eighty-nine".