21085205 has 4 divisors (see below), whose sum is σ = 25302252. Its totient is φ = 16868160.

The previous prime is 21085201. The next prime is 21085213. The reversal of 21085205 is 50258012.

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 13205956 + 7879249 = 3634^2 + 2807^2 .

It is not a de Polignac number, because 21085205 - 2² = 21085201 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 (21085201) 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, 2108516 + ... + 2108525.

It is an arithmetic number, because the mean of its divisors is an integer number (6325563).

Almost surely, 2^21085205 is an apocalyptic number.

It is an amenable number.

21085205 is a deficient number, since it is larger than the sum of its proper divisors (4217047).

21085205 is an equidigital number, since it uses as much as digits as its factorization.

21085205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4217046.

The product of its (nonzero) digits is 800, while the sum is 23.

The square root of 21085205 is about 4591.8629117168. The cubic root of 21085205 is about 276.2650476710.

The spelling of 21085205 in words is "twenty-one million, eighty-five thousand, two hundred five".