21285 has 24 divisors (see below), whose sum is σ = 41184. Its totient is φ = 10080.

The previous prime is 21283. The next prime is 21313. The reversal of 21285 is 58212.

It is not a de Polignac number, because 21285 - 2¹ = 21283 is a prime.

It is a Curzon number.

It is a congruent 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 23 ways as a sum of consecutive naturals, for example, 474 + ... + 516.

It is an arithmetic number, because the mean of its divisors is an integer number (1716).

2²¹²⁸⁵ is an apocalyptic number.

It is an amenable number.

21285 is a deficient number, since it is larger than the sum of its proper divisors (19899).

21285 is a wasteful number, since it uses less digits than its factorization.

21285 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65 (or 62 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21285 is about 145.8937969895. The cubic root of 21285 is about 27.7134898475.

Adding to 21285 its reverse (58212), we get a palindrome (79497).

The spelling of 21285 in words is "twenty-one thousand, two hundred eighty-five".