21101221 has 4 divisors (see below), whose sum is σ = 21110944. Its totient is φ = 21091500.

The previous prime is 21101219. The next prime is 21101243. The reversal of 21101221 is 12210112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21101221 - 2¹ = 21101219 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21101198 and 21101207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21101251) 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, 46 + ... + 6496.

It is an arithmetic number, because the mean of its divisors is an integer number (5277736).

Almost surely, 2^21101221 is an apocalyptic number.

It is an amenable number.

21101221 is a deficient number, since it is larger than the sum of its proper divisors (9723).

21101221 is an equidigital number, since it uses as much as digits as its factorization.

21101221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9722.

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 21101221 is about 4593.6065351747. The cubic root of 21101221 is about 276.3349788728.

Adding to 21101221 its reverse (12210112), we get a palindrome (33311333).

The spelling of 21101221 in words is "twenty-one million, one hundred one thousand, two hundred twenty-one".