21085305 has 16 divisors (see below), whose sum is σ = 33929280. Its totient is φ = 11181248.

The previous prime is 21085289. The next prime is 21085343. The reversal of 21085305 is 50358012.

It is a cyclic number.

It is not a de Polignac number, because 21085305 - 2⁴ = 21085289 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1242 + ... + 6611.

It is an arithmetic number, because the mean of its divisors is an integer number (2120580).

Almost surely, 2^21085305 is an apocalyptic number.

It is an amenable number.

21085305 is a deficient number, since it is larger than the sum of its proper divisors (12843975).

21085305 is a wasteful number, since it uses less digits than its factorization.

21085305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8040.

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 21085305 is about 4591.8738005307. The cubic root of 21085305 is about 276.2654844142.

The spelling of 21085305 in words is "twenty-one million, eighty-five thousand, three hundred five".