21530205 has 20 divisors (see below), whose sum is σ = 38595612. Its totient is φ = 11482560.

The previous prime is 21530161. The next prime is 21530227. The reversal of 21530205 is 50203512.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 11148921 + 10381284 = 3339^2 + 3222^2 .

It is not a de Polignac number, because 21530205 - 2⁷ = 21530077 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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 19 ways as a sum of consecutive naturals, for example, 26176 + ... + 26985.

Almost surely, 2^21530205 is an apocalyptic number.

It is an amenable number.

21530205 is a deficient number, since it is larger than the sum of its proper divisors (17065407).

21530205 is an equidigital number, since it uses as much as digits as its factorization.

21530205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53178 (or 53169 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21530205 is about 4640.0651935075. The cubic root of 21530205 is about 278.1950436724.

Adding to 21530205 its reverse (50203512), we get a palindrome (71733717).

The spelling of 21530205 in words is "twenty-one million, five hundred thirty thousand, two hundred five".