16428721 has 4 divisors (see below), whose sum is σ = 16437744. Its totient is φ = 16419700.

The previous prime is 16428719. The next prime is 16428743. The reversal of 16428721 is 12782461.

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, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12782461 = 67 ⋅190783.

It is a cyclic number.

It is not a de Polignac number, because 16428721 - 2¹ = 16428719 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16428701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 715 + ... + 5776.

It is an arithmetic number, because the mean of its divisors is an integer number (4109436).

Almost surely, 2^16428721 is an apocalyptic number.

It is an amenable number.

16428721 is a deficient number, since it is larger than the sum of its proper divisors (9023).

16428721 is an equidigital number, since it uses as much as digits as its factorization.

16428721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9022.

The product of its digits is 5376, while the sum is 31.

The square root of 16428721 is about 4053.2358677975. The cubic root of 16428721 is about 254.2150461461.

The spelling of 16428721 in words is "sixteen million, four hundred twenty-eight thousand, seven hundred twenty-one".