644789081 has 2 divisors, whose sum is σ = 644789082. Its totient is φ = 644789080.

The previous prime is 644789059. The next prime is 644789129. The reversal of 644789081 is 180987446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 640545481 + 4243600 = 25309^2 + 2060^2 .

It is a cyclic number.

It is not a de Polignac number, because 644789081 - 2¹⁸ = 644526937 is a prime.

It is a super-2 number, since 2×644789081² = 831505917953649122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (644789281) 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, 322394540 + 322394541.

It is an arithmetic number, because the mean of its divisors is an integer number (322394541).

Almost surely, 2^644789081 is an apocalyptic number.

It is an amenable number.

644789081 is a deficient number, since it is larger than the sum of its proper divisors (1).

644789081 is an equidigital number, since it uses as much as digits as its factorization.

644789081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 387072, while the sum is 47.

The square root of 644789081 is about 25392.6973951174. The cubic root of 644789081 is about 863.9180703812.

The spelling of 644789081 in words is "six hundred forty-four million, seven hundred eighty-nine thousand, eighty-one".