28381 has 4 divisors (see below), whose sum is σ = 28764. Its totient is φ = 28000.

The previous prime is 28351. The next prime is 28387. The reversal of 28381 is 18382.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 24025 + 4356 = 155^2 + 66^2 .

It is a cyclic number.

It is not a de Polignac number, because 28381 - 2⁵ = 28349 is a prime.

It is a super-2 number, since 2×28381² = 1610962322, which contains 22 as substring.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40 + ... + 241.

It is an arithmetic number, because the mean of its divisors is an integer number (7191).

2²⁸³⁸¹ is an apocalyptic number.

It is an amenable number.

28381 is a deficient number, since it is larger than the sum of its proper divisors (383).

28381 is a wasteful number, since it uses less digits than its factorization.

28381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 382.

The product of its digits is 384, while the sum is 22.

The square root of 28381 is about 168.4666139032. The cubic root of 28381 is about 30.5030006902.

Subtracting from 28381 its reverse (18382), we obtain a palindrome (9999).

The spelling of 28381 in words is "twenty-eight thousand, three hundred eighty-one".