138188021 has 2 divisors, whose sum is σ = 138188022. Its totient is φ = 138188020.

The previous prime is 138188009. The next prime is 138188027. The reversal of 138188021 is 120881831.

It is a happy number.

138188021 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 can be written as a sum of positive squares in only one way, i.e., 137217796 + 970225 = 11714^2 + 985^2 .

It is a cyclic number.

It is not a de Polignac number, because 138188021 - 2¹⁸ = 137925877 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138188027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69094010 + 69094011.

It is an arithmetic number, because the mean of its divisors is an integer number (69094011).

Almost surely, 2^138188021 is an apocalyptic number.

It is an amenable number.

138188021 is a deficient number, since it is larger than the sum of its proper divisors (1).

138188021 is an equidigital number, since it uses as much as digits as its factorization.

138188021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3072, while the sum is 32.

The square root of 138188021 is about 11755.3401056711. The cubic root of 138188021 is about 516.9995111404. Note that the first 3 decimals are identical.

The spelling of 138188021 in words is "one hundred thirty-eight million, one hundred eighty-eight thousand, twenty-one".