16664821 has 8 divisors (see below), whose sum is σ = 17332920. Its totient is φ = 16003008.

The previous prime is 16664807. The next prime is 16664827. The reversal of 16664821 is 12846661.

It can be written as a sum of positive squares in 4 ways, for example, as 13242321 + 3422500 = 3639^2 + 1850^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 16664821 - 2⁵ = 16664789 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 (16664827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4255 + ... + 7171.

It is an arithmetic number, because the mean of its divisors is an integer number (2166615).

Almost surely, 2^16664821 is an apocalyptic number.

It is an amenable number.

16664821 is a deficient number, since it is larger than the sum of its proper divisors (668099).

16664821 is a wasteful number, since it uses less digits than its factorization.

16664821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3143.

The product of its digits is 13824, while the sum is 34.

The square root of 16664821 is about 4082.2568513017. The cubic root of 16664821 is about 255.4270481046.

The spelling of 16664821 in words is "sixteen million, six hundred sixty-four thousand, eight hundred twenty-one".