138388021 has 4 divisors (see below), whose sum is σ = 138499200. Its totient is φ = 138276844.

The previous prime is 138387979. The next prime is 138388043. The reversal of 138388021 is 120883831.

138388021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 120883831 = 53 ⋅2280827.

It is a cyclic number.

It is not a de Polignac number, because 138388021 - 2¹⁵ = 138355253 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (138388421) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 53701 + ... + 56218.

It is an arithmetic number, because the mean of its divisors is an integer number (34624800).

Almost surely, 2^138388021 is an apocalyptic number.

It is an amenable number.

138388021 is a deficient number, since it is larger than the sum of its proper divisors (111179).

138388021 is a wasteful number, since it uses less digits than its factorization.

138388021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111178.

The product of its (nonzero) digits is 9216, while the sum is 34.

The square root of 138388021 is about 11763.8438020912. The cubic root of 138388021 is about 517.2488093016.

The spelling of 138388021 in words is "one hundred thirty-eight million, three hundred eighty-eight thousand, twenty-one".