138721 has 4 divisors (see below), whose sum is σ = 151344. Its totient is φ = 126100.

The previous prime is 138683. The next prime is 138727. The reversal of 138721 is 127831.

138721 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, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 127831 = 11 ⋅11621.

It is a cyclic number.

It is not a de Polignac number, because 138721 - 2⁹ = 138209 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 138692 and 138701.

It is not an unprimeable number, because it can be changed into a prime (138727) 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, 6295 + ... + 6316.

It is an arithmetic number, because the mean of its divisors is an integer number (37836).

2¹³⁸⁷²¹ is an apocalyptic number.

138721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

138721 is a deficient number, since it is larger than the sum of its proper divisors (12623).

138721 is a wasteful number, since it uses less digits than its factorization.

138721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12622.

The product of its digits is 336, while the sum is 22.

The square root of 138721 is about 372.4526815583. The cubic root of 138721 is about 51.7663332265.

The spelling of 138721 in words is "one hundred thirty-eight thousand, seven hundred twenty-one".