21345221 has 4 divisors (see below), whose sum is σ = 21456012. Its totient is φ = 21234432.

The previous prime is 21345211. The next prime is 21345223. The reversal of 21345221 is 12254312.

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 10048900 + 11296321 = 3170^2 + 3361^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21345221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21345193 and 21345202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21345223) 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, 55106 + ... + 55491.

It is an arithmetic number, because the mean of its divisors is an integer number (5364003).

Almost surely, 2^21345221 is an apocalyptic number.

It is an amenable number.

21345221 is a deficient number, since it is larger than the sum of its proper divisors (110791).

21345221 is a wasteful number, since it uses less digits than its factorization.

21345221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110790.

The product of its digits is 480, while the sum is 20.

The square root of 21345221 is about 4620.0888519595. The cubic root of 21345221 is about 277.3960154727.

Adding to 21345221 its reverse (12254312), we get a palindrome (33599533).

Subtracting from 21345221 its reverse (12254312), we obtain a palindrome (9090909).

The spelling of 21345221 in words is "twenty-one million, three hundred forty-five thousand, two hundred twenty-one".