21521245 has 4 divisors (see below), whose sum is σ = 25825500. Its totient is φ = 17216992.

The previous prime is 21521183. The next prime is 21521249. The reversal of 21521245 is 54212512.

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 7300804 + 14220441 = 2702^2 + 3771^2 .

It is a cyclic number.

It is not a de Polignac number, because 21521245 - 2⁷ = 21521117 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521249) 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, 2152120 + ... + 2152129.

It is an arithmetic number, because the mean of its divisors is an integer number (6456375).

Almost surely, 2^21521245 is an apocalyptic number.

It is an amenable number.

21521245 is a deficient number, since it is larger than the sum of its proper divisors (4304255).

21521245 is an equidigital number, since it uses as much as digits as its factorization.

21521245 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4304254.

The product of its digits is 800, while the sum is 22.

The square root of 21521245 is about 4639.0995893600. The cubic root of 21521245 is about 278.1564471449.

Adding to 21521245 its reverse (54212512), we get a palindrome (75733757).

The spelling of 21521245 in words is "twenty-one million, five hundred twenty-one thousand, two hundred forty-five".