212121221 has 4 divisors (see below), whose sum is σ = 228438252. Its totient is φ = 195804192.

The previous prime is 212121209. The next prime is 212121289. The reversal of 212121221 is 122121212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 67881121 + 144240100 = 8239^2 + 12010^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-212121221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 212121196 and 212121205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (212121421) 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 3 ways as a sum of consecutive naturals, for example, 8158496 + ... + 8158521.

It is an arithmetic number, because the mean of its divisors is an integer number (57109563).

Almost surely, 2^212121221 is an apocalyptic number.

It is an amenable number.

212121221 is a deficient number, since it is larger than the sum of its proper divisors (16317031).

212121221 is a wasteful number, since it uses less digits than its factorization.

212121221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16317030.

The product of its digits is 32, while the sum is 14.

The square root of 212121221 is about 14564.3819299001. The cubic root of 212121221 is about 596.3868232284.

Adding to 212121221 its reverse (122121212), we get a palindrome (334242433).

Subtracting from 212121221 its reverse (122121212), we obtain a palindrome (90000009).

It can be divided in two parts, 21212 and 1221, that multiplied together give a palindrome (25899852).

The spelling of 212121221 in words is "two hundred twelve million, one hundred twenty-one thousand, two hundred twenty-one".