21121221 has 16 divisors (see below), whose sum is σ = 31030848. Its totient is φ = 12672000.

The previous prime is 21121211. The next prime is 21121223. The reversal of 21121221 is 12212112.

It is not a de Polignac number, because 21121221 - 2¹¹ = 21119173 is a prime.

It is a super-2 number, since 2×21121221² = 892211953061682, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21121197 and 21121206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 165 + ... + 6501.

It is an arithmetic number, because the mean of its divisors is an integer number (1939428).

Almost surely, 2^21121221 is an apocalyptic number.

It is an amenable number.

21121221 is a deficient number, since it is larger than the sum of its proper divisors (9909627).

21121221 is a wasteful number, since it uses less digits than its factorization.

21121221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6452.

The product of its digits is 16, while the sum is 12.

The square root of 21121221 is about 4595.7829583217. The cubic root of 21121221 is about 276.4222558824.

Adding to 21121221 its reverse (12212112), we get a palindrome (33333333).

It can be divided in two parts, 2112 and 1221, that multiplied together give a palindrome (2578752).

The spelling of 21121221 in words is "twenty-one million, one hundred twenty-one thousand, two hundred twenty-one".