21666166 has 4 divisors (see below), whose sum is σ = 32499252. Its totient is φ = 10833082.

The previous prime is 21666149. The next prime is 21666167. The reversal of 21666166 is 66166612.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666167) 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 as a sum of consecutive naturals, namely, 5416540 + ... + 5416543.

It is an arithmetic number, because the mean of its divisors is an integer number (8124813).

Almost surely, 2^21666166 is an apocalyptic number.

21666166 is a deficient number, since it is larger than the sum of its proper divisors (10833086).

21666166 is a wasteful number, since it uses less digits than its factorization.

21666166 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10833085.

The product of its digits is 15552, while the sum is 34.

The square root of 21666166 is about 4654.6929007186. The cubic root of 21666166 is about 278.7794062296.

The spelling of 21666166 in words is "twenty-one million, six hundred sixty-six thousand, one hundred sixty-six".