21220121 has 4 divisors (see below), whose sum is σ = 22852452. Its totient is φ = 19587792.

The previous prime is 21220109. The next prime is 21220153. The reversal of 21220121 is 12102212.

It is a happy number.

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 9241600 + 11978521 = 3040^2 + 3461^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220121 - 2¹⁴ = 21203737 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21220921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 816146 + ... + 816171.

It is an arithmetic number, because the mean of its divisors is an integer number (5713113).

Almost surely, 2^21220121 is an apocalyptic number.

It is an amenable number.

21220121 is a deficient number, since it is larger than the sum of its proper divisors (1632331).

21220121 is a wasteful number, since it uses less digits than its factorization.

21220121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1632330.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21220121 is about 4606.5302560604. The cubic root of 21220121 is about 276.8530327694.

Adding to 21220121 its reverse (12102212), we get a palindrome (33322333).

The spelling of 21220121 in words is "twenty-one million, two hundred twenty thousand, one hundred twenty-one".