21055209 has 16 divisors (see below), whose sum is σ = 32148480. Its totient is φ = 12007440.

The previous prime is 21055207. The next prime is 21055213. The reversal of 21055209 is 90255012.

It is not a de Polignac number, because 21055209 - 2¹ = 21055207 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21055207) 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 15 ways as a sum of consecutive naturals, for example, 18754 + ... + 19844.

It is an arithmetic number, because the mean of its divisors is an integer number (2009280).

Almost surely, 2^21055209 is an apocalyptic number.

It is an amenable number.

21055209 is a deficient number, since it is larger than the sum of its proper divisors (11093271).

21055209 is a wasteful number, since it uses less digits than its factorization.

21055209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2020.

The product of its (nonzero) digits is 900, while the sum is 24.

The square root of 21055209 is about 4588.5955367629. The cubic root of 21055209 is about 276.1339797946.

The spelling of 21055209 in words is "twenty-one million, fifty-five thousand, two hundred nine".