21109221 has 32 divisors (see below), whose sum is σ = 36295680. Its totient is φ = 11875248.

The previous prime is 21109217. The next prime is 21109229. The reversal of 21109221 is 12290112.

It is not a de Polignac number, because 21109221 - 2² = 21109217 is a prime.

It is a super-2 number, since 2×21109221² = 891198422453682, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21109194 and 21109203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21109229) 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 31 ways as a sum of consecutive naturals, for example, 11830 + ... + 13496.

It is an arithmetic number, because the mean of its divisors is an integer number (1134240).

Almost surely, 2^21109221 is an apocalyptic number.

21109221 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21109221 is a deficient number, since it is larger than the sum of its proper divisors (15186459).

21109221 is a wasteful number, since it uses less digits than its factorization.

21109221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1750 (or 1744 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 21109221 is about 4594.4772281512. The cubic root of 21109221 is about 276.3698962916.

Adding to 21109221 its reverse (12290112), we get a palindrome (33399333).

The spelling of 21109221 in words is "twenty-one million, one hundred nine thousand, two hundred twenty-one".