16556721 has 8 divisors (see below), whose sum is σ = 22138560. Its totient is φ = 11006352.

The previous prime is 16556719. The next prime is 16556753. The reversal of 16556721 is 12765561.

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

It is not a de Polignac number, because 16556721 - 2¹ = 16556719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (16556791) 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 7 ways as a sum of consecutive naturals, for example, 6610 + ... + 8763.

It is an arithmetic number, because the mean of its divisors is an integer number (2767320).

Almost surely, 2^16556721 is an apocalyptic number.

It is an amenable number.

16556721 is a deficient number, since it is larger than the sum of its proper divisors (5581839).

16556721 is a wasteful number, since it uses less digits than its factorization.

16556721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15735.

The product of its digits is 12600, while the sum is 33.

The square root of 16556721 is about 4068.9950847844. The cubic root of 16556721 is about 254.8735551504.

The spelling of 16556721 in words is "sixteen million, five hundred fifty-six thousand, seven hundred twenty-one".