15981 has 8 divisors (see below), whose sum is σ = 24384. Its totient is φ = 9120.

The previous prime is 15973. The next prime is 15991. The reversal of 15981 is 18951.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 15981 - 2³ = 15973 is a prime.

It is a super-2 number, since 2×15981² = 510784722, which contains 22 as substring.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

15981 is a lucky number.

It is a nialpdrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15901) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 360 + ... + 401.

It is an arithmetic number, because the mean of its divisors is an integer number (3048).

2¹⁵⁹⁸¹ is an apocalyptic number.

It is an amenable number.

15981 is a deficient number, since it is larger than the sum of its proper divisors (8403).

15981 is an equidigital number, since it uses as much as digits as its factorization.

15981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 771.

The product of its digits is 360, while the sum is 24.

The square root of 15981 is about 126.4159800025. The cubic root of 15981 is about 25.1884426721.

The spelling of 15981 in words is "fifteen thousand, nine hundred eighty-one".