21704521 has 2 divisors, whose sum is σ = 21704522. Its totient is φ = 21704520.

The previous prime is 21704483. The next prime is 21704531. The reversal of 21704521 is 12540712.

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., 19713600 + 1990921 = 4440^2 + 1411^2 .

It is a cyclic number.

It is not a de Polignac number, because 21704521 - 2⁹ = 21704009 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21704492 and 21704501.

It is not a weakly prime, because it can be changed into another prime (21704531) 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, 10852260 + 10852261.

It is an arithmetic number, because the mean of its divisors is an integer number (10852261).

Almost surely, 2^21704521 is an apocalyptic number.

It is an amenable number.

21704521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21704521 is an equidigital number, since it uses as much as digits as its factorization.

21704521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21704521 is about 4658.8111144368. The cubic root of 21704521 is about 278.9438143477.

The spelling of 21704521 in words is "twenty-one million, seven hundred four thousand, five hundred twenty-one".