16666221 has 32 divisors (see below), whose sum is σ = 26635392. Its totient is φ = 9135360.

The previous prime is 16666219. The next prime is 16666231. The reversal of 16666221 is 12266661.

It is not a de Polignac number, because 16666221 - 2¹ = 16666219 is a prime.

It is a super-3 number, since 3×16666221³ (a number of 23 digits) contains 333 as substring.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16666201) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 22371 + ... + 23103.

It is an arithmetic number, because the mean of its divisors is an integer number (832356).

Almost surely, 2^16666221 is an apocalyptic number.

16666221 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

16666221 is a deficient number, since it is larger than the sum of its proper divisors (9969171).

16666221 is a wasteful number, since it uses less digits than its factorization.

16666221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 813.

The product of its digits is 5184, while the sum is 30.

The square root of 16666221 is about 4082.4283214773. The cubic root of 16666221 is about 255.4342006538.

It can be divided in two parts, 1666 and 6221, that added together give a palindrome (7887).

The spelling of 16666221 in words is "sixteen million, six hundred sixty-six thousand, two hundred twenty-one".