16404721 has 4 divisors (see below), whose sum is σ = 16473600. Its totient is φ = 16335844.

The previous prime is 16404709. The next prime is 16404757. The reversal of 16404721 is 12740461.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 16404721 - 2⁷ = 16404593 is a prime.

It is a super-2 number, since 2×16404721² = 538229742175682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16404761) 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, 34081 + ... + 34558.

It is an arithmetic number, because the mean of its divisors is an integer number (4118400).

Almost surely, 2^16404721 is an apocalyptic number.

It is an amenable number.

16404721 is a deficient number, since it is larger than the sum of its proper divisors (68879).

16404721 is an equidigital number, since it uses as much as digits as its factorization.

16404721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68878.

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 16404721 is about 4050.2741882495. The cubic root of 16404721 is about 254.0911952694.

The spelling of 16404721 in words is "sixteen million, four hundred four thousand, seven hundred twenty-one".