181561 has 4 divisors (see below), whose sum is σ = 185472. Its totient is φ = 177652.

The previous prime is 181553. The next prime is 181603. The reversal of 181561 is 165181.

181561 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.

It is a cyclic number.

It is not a de Polignac number, because 181561 - 2³ = 181553 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (181501) 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, 1885 + ... + 1978.

It is an arithmetic number, because the mean of its divisors is an integer number (46368).

2¹⁸¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

181561 is a deficient number, since it is larger than the sum of its proper divisors (3911).

181561 is an equidigital number, since it uses as much as digits as its factorization.

181561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3910.

The product of its digits is 240, while the sum is 22.

The square root of 181561 is about 426.0997535789. The cubic root of 181561 is about 56.6249096448.

The spelling of 181561 in words is "one hundred eighty-one thousand, five hundred sixty-one".