21212171 has 4 divisors (see below), whose sum is σ = 21450600. Its totient is φ = 20973744.

The previous prime is 21212161. The next prime is 21212179. The reversal of 21212171 is 17121212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21212171 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21212179) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 119081 + ... + 119258.

It is an arithmetic number, because the mean of its divisors is an integer number (5362650).

Almost surely, 2^21212171 is an apocalyptic number.

21212171 is a deficient number, since it is larger than the sum of its proper divisors (238429).

21212171 is an equidigital number, since it uses as much as digits as its factorization.

21212171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 238428.

The product of its digits is 56, while the sum is 17.

The square root of 21212171 is about 4605.6672697884. The cubic root of 21212171 is about 276.8184546360.

Adding to 21212171 its reverse (17121212), we get a palindrome (38333383).

The spelling of 21212171 in words is "twenty-one million, two hundred twelve thousand, one hundred seventy-one".