16555221 has 6 divisors (see below), whose sum is σ = 23913110. Its totient is φ = 11036808.

The previous prime is 16555219. The next prime is 16555249. The reversal of 16555221 is 12255561.

16555221 is a `hidden beast` number, since 1 + 655 + 5 + 2 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 13950225 + 2604996 = 3735^2 + 1614^2 .

It is not a de Polignac number, because 16555221 - 2¹ = 16555219 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 (16555621) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 919726 + ... + 919743.

Almost surely, 2^16555221 is an apocalyptic number.

It is an amenable number.

16555221 is a deficient number, since it is larger than the sum of its proper divisors (7357889).

16555221 is a wasteful number, since it uses less digits than its factorization.

16555221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1839475 (or 1839472 counting only the distinct ones).

The product of its digits is 3000, while the sum is 27.

The square root of 16555221 is about 4068.8107599150. The cubic root of 16555221 is about 254.8658579363.

The spelling of 16555221 in words is "sixteen million, five hundred fifty-five thousand, two hundred twenty-one".