15666221 has 8 divisors (see below), whose sum is σ = 15971904. Its totient is φ = 15363040.

The previous prime is 15666199. The next prime is 15666227. The reversal of 15666221 is 12266651.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-15666221 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 (15666227) 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, 16070 + ... + 17016.

It is an arithmetic number, because the mean of its divisors is an integer number (1996488).

Almost surely, 2^15666221 is an apocalyptic number.

It is an amenable number.

15666221 is a deficient number, since it is larger than the sum of its proper divisors (305683).

15666221 is an equidigital number, since it uses as much as digits as its factorization.

15666221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1251.

The product of its digits is 4320, while the sum is 29.

The square root of 15666221 is about 3958.0577307563. The cubic root of 15666221 is about 250.2196522883.

The spelling of 15666221 in words is "fifteen million, six hundred sixty-six thousand, two hundred twenty-one".