138691 has 4 divisors (see below), whose sum is σ = 158512. Its totient is φ = 118872.

The previous prime is 138683. The next prime is 138727. The reversal of 138691 is 196831.

It is a happy number.

138691 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.

It is a cyclic number.

It is not a de Polignac number, because 138691 - 2³ = 138683 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (138641) 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, 9900 + ... + 9913.

It is an arithmetic number, because the mean of its divisors is an integer number (39628).

2¹³⁸⁶⁹¹ is an apocalyptic number.

138691 is a deficient number, since it is larger than the sum of its proper divisors (19821).

138691 is an equidigital number, since it uses as much as digits as its factorization.

138691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19820.

The product of its digits is 1296, while the sum is 28.

The square root of 138691 is about 372.4124058084. The cubic root of 138691 is about 51.7626012706.

The spelling of 138691 in words is "one hundred thirty-eight thousand, six hundred ninety-one".