138228921 has 12 divisors (see below), whose sum is σ = 211409172. Its totient is φ = 86731776.

The previous prime is 138228911. The next prime is 138228943. The reversal of 138228921 is 129822831.

138228921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 120890025 + 17338896 = 10995^2 + 4164^2 .

It is not a de Polignac number, because 138228921 - 2⁵ = 138228889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (138228911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 451576 + ... + 451881.

It is an arithmetic number, because the mean of its divisors is an integer number (17617431).

Almost surely, 2^138228921 is an apocalyptic number.

It is an amenable number.

138228921 is a deficient number, since it is larger than the sum of its proper divisors (73180251).

138228921 is a wasteful number, since it uses less digits than its factorization.

138228921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 903480 (or 903477 counting only the distinct ones).

The product of its digits is 13824, while the sum is 36.

The square root of 138228921 is about 11757.0796118764. The cubic root of 138228921 is about 517.0505121704.

It can be divided in two parts, 1382 and 28921, that added together give a palindrome (30303).

The spelling of 138228921 in words is "one hundred thirty-eight million, two hundred twenty-eight thousand, nine hundred twenty-one".