21212166 has 16 divisors (see below), whose sum is σ = 43887600. Its totient is φ = 6826848.

The previous prime is 21212161. The next prime is 21212179. The reversal of 21212166 is 66121212.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212161) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 60781 + ... + 61128.

It is an arithmetic number, because the mean of its divisors is an integer number (2742975).

Almost surely, 2^21212166 is an apocalyptic number.

21212166 is an abundant number, since it is smaller than the sum of its proper divisors (22675434).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21212166 is a wasteful number, since it uses less digits than its factorization.

21212166 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 121943.

The product of its digits is 288, while the sum is 21.

The square root of 21212166 is about 4605.6667269788. Note that the first 3 decimals coincide. The cubic root of 21212166 is about 276.8184328860.

Adding to 21212166 its reverse (66121212), we get a palindrome (87333378).

It can be divided in two parts, 212121 and 66, that multiplied together give a triangular number (13999986 = T₅₂₉₁).

The spelling of 21212166 in words is "twenty-one million, two hundred twelve thousand, one hundred sixty-six".