21205253 has 4 divisors (see below), whose sum is σ = 21415308. Its totient is φ = 20995200.

The previous prime is 21205243. The next prime is 21205279. The reversal of 21205253 is 35250212.

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 11607649 + 9597604 = 3407^2 + 3098^2 .

It is a cyclic number.

It is not a de Polignac number, because 21205253 - 2⁴ = 21205237 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 (21205213) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104876 + ... + 105077.

It is an arithmetic number, because the mean of its divisors is an integer number (5353827).

Almost surely, 2^21205253 is an apocalyptic number.

It is an amenable number.

21205253 is a deficient number, since it is larger than the sum of its proper divisors (210055).

21205253 is a wasteful number, since it uses less digits than its factorization.

21205253 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210054.

The product of its (nonzero) digits is 600, while the sum is 20.

The square root of 21205253 is about 4604.9161773044. The cubic root of 21205253 is about 276.7883581049.

Adding to 21205253 its reverse (35250212), we get a palindrome (56455465).

The spelling of 21205253 in words is "twenty-one million, two hundred five thousand, two hundred fifty-three".