2181 has 4 divisors (see below), whose sum is σ = 2912. Its totient is φ = 1452.

The previous prime is 2179. The next prime is 2203. The reversal of 2181 is 1812.

It is a happy number.

2181 is nontrivially palindromic in base 14.

2181 is an esthetic number in base 13, because in such base its adjacent digits differ by 1.

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.

It is not a de Polignac number, because 2181 - 2¹ = 2179 is a prime.

It is a super-2 number, since 2×2181² = 9513522, which contains 22 as substring.

It is a D-number.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

2181 is an undulating number in base 14.

It is a Curzon number.

It is a nialpdrome in base 3, base 5, base 13 and base 16.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 2181.

It is not an unprimeable number, because it can be changed into a prime (2111) 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, 361 + ... + 366.

It is an arithmetic number, because the mean of its divisors is an integer number (728).

It is an amenable number.

2181 is a deficient number, since it is larger than the sum of its proper divisors (731).

2181 is an equidigital number, since it uses as much as digits as its factorization.

2181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 730.

The product of its digits is 16, while the sum is 12.

The square root of 2181 is about 46.7011777153. The cubic root of 2181 is about 12.9683648940.

Adding to 2181 its product of digits (16), we get a cube (2197 = 13³).

Adding to 2181 its reverse (1812), we get a palindrome (3993).

The spelling of 2181 in words is "two thousand, one hundred eighty-one".