15721 has 4 divisors (see below), whose sum is σ = 16000. Its totient is φ = 15444.

The previous prime is 15683. The next prime is 15727. The reversal of 15721 is 12751.

15721 is digitally balanced in base 3, 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: 12751 = 41 ⋅311.

It is a cyclic number.

It is not a de Polignac number, because 15721 - 2¹³ = 7529 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 15695 and 15704.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15727) 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, 21 + ... + 178.

It is an arithmetic number, because the mean of its divisors is an integer number (4000).

It is an amenable number.

15721 is a deficient number, since it is larger than the sum of its proper divisors (279).

15721 is an equidigital number, since it uses as much as digits as its factorization.

15721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 278.

The product of its digits is 70, while the sum is 16.

The square root of 15721 is about 125.3834119810. The cubic root of 15721 is about 25.0510954989.

Subtracting from 15721 its product of digits (70), we obtain a palindrome (15651).

The spelling of 15721 in words is "fifteen thousand, seven hundred twenty-one".