21057521 has 2 divisors, whose sum is σ = 21057522. Its totient is φ = 21057520.

The previous prime is 21057511. The next prime is 21057523. The reversal of 21057521 is 12575012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10817521 + 10240000 = 3289^2 + 3200^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21057521 is a prime.

Together with 21057523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21057523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10528760 + 10528761.

It is an arithmetic number, because the mean of its divisors is an integer number (10528761).

Almost surely, 2^21057521 is an apocalyptic number.

It is an amenable number.

21057521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21057521 is an equidigital number, since it uses as much as digits as its factorization.

21057521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21057521 is about 4588.8474587853. The cubic root of 21057521 is about 276.1440865319.

The spelling of 21057521 in words is "twenty-one million, fifty-seven thousand, five hundred twenty-one".