138213821 has 4 divisors (see below), whose sum is σ = 138915612. Its totient is φ = 137512032.

The previous prime is 138213811. The next prime is 138213863. The reversal of 138213821 is 128312831.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 136562596 + 1651225 = 11686^2 + 1285^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-138213821 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 (138213811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 350600 + ... + 350993.

It is an arithmetic number, because the mean of its divisors is an integer number (34728903).

Almost surely, 2^138213821 is an apocalyptic number.

It is an amenable number.

138213821 is a deficient number, since it is larger than the sum of its proper divisors (701791).

138213821 is an equidigital number, since it uses as much as digits as its factorization.

138213821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 701790.

The product of its digits is 2304, while the sum is 29.

The square root of 138213821 is about 11756.4374280647. The cubic root of 138213821 is about 517.0316841109.

The spelling of 138213821 in words is "one hundred thirty-eight million, two hundred thirteen thousand, eight hundred twenty-one".