15781 has 4 divisors (see below), whose sum is σ = 16192. Its totient is φ = 15372.

The previous prime is 15773. The next prime is 15787. The reversal of 15781 is 18751.

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: 18751 = 17 ⋅1103.

It is a cyclic number.

It is not a de Polignac number, because 15781 - 2³ = 15773 is a prime.

It is a super-2 number, since 2×15781² = 498079922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15787) 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, 141 + ... + 226.

It is an arithmetic number, because the mean of its divisors is an integer number (4048).

2¹⁵⁷⁸¹ is an apocalyptic number.

It is an amenable number.

15781 is a deficient number, since it is larger than the sum of its proper divisors (411).

15781 is an equidigital number, since it uses as much as digits as its factorization.

15781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 410.

The product of its digits is 280, while the sum is 22.

The square root of 15781 is about 125.6224502229. The cubic root of 15781 is about 25.0829246361.

Adding to 15781 its product of digits (280), we get a palindrome (16061).

The spelling of 15781 in words is "fifteen thousand, seven hundred eighty-one".