638909989 has 2 divisors, whose sum is σ = 638909990. Its totient is φ = 638909988.

The previous prime is 638909987. The next prime is 638910001. The reversal of 638909989 is 989909836.

638909989 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., 626250625 + 12659364 = 25025^2 + 3558^2 .

It is a cyclic number.

It is not a de Polignac number, because 638909989 - 2¹ = 638909987 is a prime.

Together with 638909987, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638909987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319454994 + 319454995.

It is an arithmetic number, because the mean of its divisors is an integer number (319454995).

Almost surely, 2^638909989 is an apocalyptic number.

It is an amenable number.

638909989 is a deficient number, since it is larger than the sum of its proper divisors (1).

638909989 is an equidigital number, since it uses as much as digits as its factorization.

638909989 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7558272, while the sum is 61.

The square root of 638909989 is about 25276.6688667633. The cubic root of 638909989 is about 861.2843568525.

The spelling of 638909989 in words is "six hundred thirty-eight million, nine hundred nine thousand, nine hundred eighty-nine".