21289 has 4 divisors (see below), whose sum is σ = 21700. Its totient is φ = 20880.

The previous prime is 21283. The next prime is 21313. The reversal of 21289 is 98212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6889 + 14400 = 83^2 + 120^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 114 + ... + 235.

It is an arithmetic number, because the mean of its divisors is an integer number (5425).

2²¹²⁸⁹ is an apocalyptic number.

It is an amenable number.

21289 is a deficient number, since it is larger than the sum of its proper divisors (411).

21289 is an equidigital number, since it uses as much as digits as its factorization.

21289 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 410.

The product of its digits is 288, while the sum is 22.

The square root of 21289 is about 145.9075049475. The cubic root of 21289 is about 27.7152257651.

The spelling of 21289 in words is "twenty-one thousand, two hundred eighty-nine".