638388021 has 16 divisors (see below), whose sum is σ = 873892800. Its totient is φ = 414360960.

The previous prime is 638388013. The next prime is 638388031. The reversal of 638388021 is 120883836.

It is not a de Polignac number, because 638388021 - 2³ = 638388013 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638388031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5505 + ... + 36153.

It is an arithmetic number, because the mean of its divisors is an integer number (54618300).

Almost surely, 2^638388021 is an apocalyptic number.

It is an amenable number.

638388021 is a deficient number, since it is larger than the sum of its proper divisors (235504779).

638388021 is a wasteful number, since it uses less digits than its factorization.

638388021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30836.

The product of its (nonzero) digits is 55296, while the sum is 39.

The square root of 638388021 is about 25266.3416623776. The cubic root of 638388021 is about 861.0497461548.

The spelling of 638388021 in words is "six hundred thirty-eight million, three hundred eighty-eight thousand, twenty-one".