21242521 has 2 divisors, whose sum is σ = 21242522. Its totient is φ = 21242520.

The previous prime is 21242519. The next prime is 21242527. The reversal of 21242521 is 12524212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20602521 + 640000 = 4539^2 + 800^2 .

It is a cyclic number.

It is not a de Polignac number, because 21242521 - 2¹ = 21242519 is a prime.

Together with 21242519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21242527) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10621260 + 10621261.

It is an arithmetic number, because the mean of its divisors is an integer number (10621261).

Almost surely, 2^21242521 is an apocalyptic number.

It is an amenable number.

21242521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21242521 is an equidigital number, since it uses as much as digits as its factorization.

21242521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 320, while the sum is 19.

The square root of 21242521 is about 4608.9609458098. The cubic root of 21242521 is about 276.9504140411.

Adding to 21242521 its reverse (12524212), we get a palindrome (33766733).

The spelling of 21242521 in words is "twenty-one million, two hundred forty-two thousand, five hundred twenty-one".