16566721 has 4 divisors (see below), whose sum is σ = 17541252. Its totient is φ = 15592192.

The previous prime is 16566709. The next prime is 16566731. The reversal of 16566721 is 12766561.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12110400 + 4456321 = 3480^2 + 2111^2 .

It is a cyclic number.

It is not a de Polignac number, because 16566721 - 2¹⁷ = 16435649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16566731) 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 3 ways as a sum of consecutive naturals, for example, 487240 + ... + 487273.

It is an arithmetic number, because the mean of its divisors is an integer number (4385313).

Almost surely, 2^16566721 is an apocalyptic number.

It is an amenable number.

16566721 is a deficient number, since it is larger than the sum of its proper divisors (974531).

16566721 is an equidigital number, since it uses as much as digits as its factorization.

16566721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 974530.

The product of its digits is 15120, while the sum is 34.

The square root of 16566721 is about 4070.2237039259. The cubic root of 16566721 is about 254.9248580341.

The spelling of 16566721 in words is "sixteen million, five hundred sixty-six thousand, seven hundred twenty-one".