21208205 has 4 divisors (see below), whose sum is σ = 25449852. Its totient is φ = 16966560.

The previous prime is 21208183. The next prime is 21208259. The reversal of 21208205 is 50280212.

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 12482089 + 8726116 = 3533^2 + 2954^2 .

It is not a de Polignac number, because 21208205 - 2¹⁶ = 21142669 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120816 + ... + 2120825.

It is an arithmetic number, because the mean of its divisors is an integer number (6362463).

Almost surely, 2^21208205 is an apocalyptic number.

It is an amenable number.

21208205 is a deficient number, since it is larger than the sum of its proper divisors (4241647).

21208205 is an equidigital number, since it uses as much as digits as its factorization.

21208205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241646.

The product of its (nonzero) digits is 320, while the sum is 20.

The square root of 21208205 is about 4605.2366931570. The cubic root of 21208205 is about 276.8012014841.

Adding to 21208205 its reverse (50280212), we get a palindrome (71488417).

The spelling of 21208205 in words is "twenty-one million, two hundred eight thousand, two hundred five".