638437991 has 2 divisors, whose sum is σ = 638437992. Its totient is φ = 638437990.

The previous prime is 638437973. The next prime is 638437993. The reversal of 638437991 is 199734836.

638437991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 638437991 - 2⁶ = 638437927 is a prime.

Together with 638437993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638437993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319218995 + 319218996.

It is an arithmetic number, because the mean of its divisors is an integer number (319218996).

Almost surely, 2^638437991 is an apocalyptic number.

638437991 is a deficient number, since it is larger than the sum of its proper divisors (1).

638437991 is an equidigital number, since it uses as much as digits as its factorization.

638437991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 979776, while the sum is 50.

The square root of 638437991 is about 25267.3305079900. The cubic root of 638437991 is about 861.0722118715.

The spelling of 638437991 in words is "six hundred thirty-eight million, four hundred thirty-seven thousand, nine hundred ninety-one".