15681 has 4 divisors (see below), whose sum is σ = 20912. Its totient is φ = 10452.

The previous prime is 15679. The next prime is 15683. The reversal of 15681 is 18651.

15681 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: 18651 = 3 ⋅6217.

It is an interprime number because it is at equal distance from previous prime (15679) and next prime (15683).

It is not a de Polignac number, because 15681 - 2¹ = 15679 is a prime.

It is a super-2 number, since 2×15681² = 491787522, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2611 + ... + 2616.

It is an arithmetic number, because the mean of its divisors is an integer number (5228).

2¹⁵⁶⁸¹ is an apocalyptic number.

It is an amenable number.

15681 is a deficient number, since it is larger than the sum of its proper divisors (5231).

15681 is an equidigital number, since it uses as much as digits as its factorization.

15681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5230.

The product of its digits is 240, while the sum is 21.

The square root of 15681 is about 125.2237996549. The cubic root of 15681 is about 25.0298310568.

It can be divided in two parts, 15 and 681, that added together give a palindrome (696).

The spelling of 15681 in words is "fifteen thousand, six hundred eighty-one".