20381 has 4 divisors (see below), whose sum is σ = 20700. Its totient is φ = 20064.

The previous prime is 20369. The next prime is 20389. The reversal of 20381 is 18302.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18302 = 2 ⋅9151.

It can be written as a sum of positive squares in 2 ways, for example, as 12100 + 8281 = 110^2 + 91^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20381 is a prime.

It is a super-2 number, since 2×20381² = 830770322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20389) 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, 26 + ... + 203.

It is an arithmetic number, because the mean of its divisors is an integer number (5175).

2²⁰³⁸¹ is an apocalyptic number.

It is an amenable number.

20381 is a deficient number, since it is larger than the sum of its proper divisors (319).

20381 is an equidigital number, since it uses as much as digits as its factorization.

20381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 318.

The product of its (nonzero) digits is 48, while the sum is 14.

The square root of 20381 is about 142.7620397725. The cubic root of 20381 is about 27.3154586022.

Adding to 20381 its reverse (18302), we get a palindrome (38683).

The spelling of 20381 in words is "twenty thousand, three hundred eighty-one".