21528217 has 2 divisors, whose sum is σ = 21528218. Its totient is φ = 21528216.

The previous prime is 21528193. The next prime is 21528223. The reversal of 21528217 is 71282512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21492496 + 35721 = 4636^2 + 189^2 .

It is a cyclic number.

It is not a de Polignac number, because 21528217 - 2¹⁹ = 21003929 is a prime.

It is not a weakly prime, because it can be changed into another prime (21528257) 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, 10764108 + 10764109.

It is an arithmetic number, because the mean of its divisors is an integer number (10764109).

Almost surely, 2^21528217 is an apocalyptic number.

It is an amenable number.

21528217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21528217 is an equidigital number, since it uses as much as digits as its factorization.

21528217 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2240, while the sum is 28.

The square root of 21528217 is about 4639.8509674342. The cubic root of 21528217 is about 278.1864809923.

The spelling of 21528217 in words is "twenty-one million, five hundred twenty-eight thousand, two hundred seventeen".