138805021 has 4 divisors (see below), whose sum is σ = 139524412. Its totient is φ = 138085632.

The previous prime is 138805003. The next prime is 138805027. The reversal of 138805021 is 120508831.

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 94848121 + 43956900 = 9739^2 + 6630^2 .

It is a cyclic number.

It is not a de Polignac number, because 138805021 - 2⁷ = 138804893 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 (138805027) 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, 359406 + ... + 359791.

It is an arithmetic number, because the mean of its divisors is an integer number (34881103).

Almost surely, 2^138805021 is an apocalyptic number.

It is an amenable number.

138805021 is a deficient number, since it is larger than the sum of its proper divisors (719391).

138805021 is an equidigital number, since it uses as much as digits as its factorization.

138805021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 719390.

The product of its (nonzero) digits is 1920, while the sum is 28.

The square root of 138805021 is about 11781.5542692804. The cubic root of 138805021 is about 517.7678245249.

The spelling of 138805021 in words is "one hundred thirty-eight million, eight hundred five thousand, twenty-one".