18561 has 8 divisors (see below), whose sum is σ = 25920. Its totient is φ = 11792.

The previous prime is 18553. The next prime is 18583. The reversal of 18561 is 16581.

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

It is a cyclic number.

It is not a de Polignac number, because 18561 - 2³ = 18553 is a prime.

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

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18521) 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, 66 + ... + 203.

It is an arithmetic number, because the mean of its divisors is an integer number (3240).

2¹⁸⁵⁶¹ is an apocalyptic number.

It is an amenable number.

18561 is a deficient number, since it is larger than the sum of its proper divisors (7359).

18561 is a wasteful number, since it uses less digits than its factorization.

18561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 295.

The product of its digits is 240, while the sum is 21.

The square root of 18561 is about 136.2387610043. The cubic root of 18561 is about 26.4768992940.

The spelling of 18561 in words is "eighteen thousand, five hundred sixty-one".