20181 has 12 divisors (see below), whose sum is σ = 31776. Its totient is φ = 11160.

The previous prime is 20177. The next prime is 20183. The reversal of 20181 is 18102.

It is a happy number.

20181 is nontrivially palindromic in base 5.

It is not a de Polignac number, because 20181 - 2² = 20177 is a prime.

It is a super-2 number, since 2×20181² = 814545522, which contains 22 as substring.

20181 is a lucky number.

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 20181.

It is not an unprimeable number, because it can be changed into a prime (20183) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 636 + ... + 666.

It is an arithmetic number, because the mean of its divisors is an integer number (2648).

2²⁰¹⁸¹ is an apocalyptic number.

20181 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20181 is a deficient number, since it is larger than the sum of its proper divisors (11595).

20181 is an equidigital number, since it uses as much as digits as its factorization.

20181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72 (or 41 counting only the distinct ones).

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

The square root of 20181 is about 142.0598465436. The cubic root of 20181 is about 27.2258153124.

Adding to 20181 its reverse (18102), we get a palindrome (38283).

It can be divided in two parts, 201 and 81, that added together give a palindrome (282).

The spelling of 20181 in words is "twenty thousand, one hundred eighty-one".