28981 has 4 divisors (see below), whose sum is σ = 29452. Its totient is φ = 28512.

The previous prime is 28979. The next prime is 29009. The reversal of 28981 is 18982.

It is the 70-th star number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18982 = 2 ⋅9491.

It can be written as a sum of positive squares in 2 ways, for example, as 17956 + 11025 = 134^2 + 105^2 .

It is a cyclic number.

It is not a de Polignac number, because 28981 - 2¹ = 28979 is a prime.

It is a super-2 number, since 2×28981² = 1679796722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28901) 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, 126 + ... + 271.

It is an arithmetic number, because the mean of its divisors is an integer number (7363).

2²⁸⁹⁸¹ is an apocalyptic number.

It is an amenable number.

28981 is a deficient number, since it is larger than the sum of its proper divisors (471).

28981 is an equidigital number, since it uses as much as digits as its factorization.

28981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 470.

The product of its digits is 1152, while the sum is 28.

The square root of 28981 is about 170.2380685981. The cubic root of 28981 is about 30.7164571336.

Subtracting from 28981 its reverse (18982), we obtain a palindrome (9999).

It can be divided in two parts, 289 and 81, that multiplied together give a square (23409 = 153²).

The spelling of 28981 in words is "twenty-eight thousand, nine hundred eighty-one".