181921 has 4 divisors (see below), whose sum is σ = 183700. Its totient is φ = 180144.

The previous prime is 181919. The next prime is 181927. The reversal of 181921 is 129181.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 112225 + 69696 = 335^2 + 264^2 .

It is a cyclic number.

It is not a de Polignac number, because 181921 - 2¹ = 181919 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 181892 and 181901.

It is not an unprimeable number, because it can be changed into a prime (181927) 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, 726 + ... + 943.

It is an arithmetic number, because the mean of its divisors is an integer number (45925).

2¹⁸¹⁹²¹ is an apocalyptic number.

It is an amenable number.

181921 is a deficient number, since it is larger than the sum of its proper divisors (1779).

181921 is a wasteful number, since it uses less digits than its factorization.

181921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1778.

The product of its digits is 144, while the sum is 22.

The square root of 181921 is about 426.5219806763. The cubic root of 181921 is about 56.6623103149.

The spelling of 181921 in words is "one hundred eighty-one thousand, nine hundred twenty-one".