21085 has 4 divisors (see below), whose sum is σ = 25308. Its totient is φ = 16864.

The previous prime is 21067. The next prime is 21089. The reversal of 21085 is 58012.

It is a happy number.

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 13689 + 7396 = 117^2 + 86^2 .

It is a cyclic number.

It is not a de Polignac number, because 21085 - 2¹¹ = 19037 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21089) 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, 2104 + ... + 2113.

It is an arithmetic number, because the mean of its divisors is an integer number (6327).

2²¹⁰⁸⁵ is an apocalyptic number.

It is an amenable number.

21085 is a deficient number, since it is larger than the sum of its proper divisors (4223).

21085 is an equidigital number, since it uses as much as digits as its factorization.

21085 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4222.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21085 is about 145.2067491544. The cubic root of 21085 is about 27.6264152343.

Adding to 21085 its reverse (58012), we get a palindrome (79097).

The spelling of 21085 in words is "twenty-one thousand, eighty-five".