16566021 has 6 divisors (see below), whose sum is σ = 23928710. Its totient is φ = 11044008.

The previous prime is 16566019. The next prime is 16566023. The reversal of 16566021 is 12066561.

It is a happy number.

16566021 is a `hidden beast` number, since 1 + 6 + 56 + 602 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (16566019) and next prime (16566023).

It can be written as a sum of positive squares in only one way, i.e., 13793796 + 2772225 = 3714^2 + 1665^2 .

It is not a de Polignac number, because 16566021 - 2¹ = 16566019 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16566023) 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 in 5 ways as a sum of consecutive naturals, for example, 920326 + ... + 920343.

Almost surely, 2^16566021 is an apocalyptic number.

It is an amenable number.

16566021 is a deficient number, since it is larger than the sum of its proper divisors (7362689).

16566021 is a wasteful number, since it uses less digits than its factorization.

16566021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1840675 (or 1840672 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 16566021 is about 4070.1377126579. The cubic root of 16566021 is about 254.9212675043.

The spelling of 16566021 in words is "sixteen million, five hundred sixty-six thousand, twenty-one".