644239993 has 2 divisors, whose sum is σ = 644239994. Its totient is φ = 644239992.

The previous prime is 644239991. The next prime is 644240033. The reversal of 644239993 is 399932446.

644239993 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 641507584 + 2732409 = 25328^2 + 1653^2 .

It is a cyclic number.

It is not a de Polignac number, because 644239993 - 2¹ = 644239991 is a prime.

Together with 644239991, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (644239991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322119996 + 322119997.

It is an arithmetic number, because the mean of its divisors is an integer number (322119997).

Almost surely, 2^644239993 is an apocalyptic number.

It is an amenable number.

644239993 is a deficient number, since it is larger than the sum of its proper divisors (1).

644239993 is an equidigital number, since it uses as much as digits as its factorization.

644239993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1259712, while the sum is 49.

The square root of 644239993 is about 25381.8831649663. The cubic root of 644239993 is about 863.6727696172.

The spelling of 644239993 in words is "six hundred forty-four million, two hundred thirty-nine thousand, nine hundred ninety-three".