21320221 has 4 divisors (see below), whose sum is σ = 22960252. Its totient is φ = 19680192.

The previous prime is 21320213. The next prime is 21320239. The reversal of 21320221 is 12202312.

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 4056196 + 17264025 = 2014^2 + 4155^2 .

It is a cyclic number.

It is not a de Polignac number, because 21320221 - 2³ = 21320213 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13), and also a Moran number because the ratio is a prime number: 1640017 = 21320221 / (2 + 1 + 3 + 2 + 0 + 2 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21320021) 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 3 ways as a sum of consecutive naturals, for example, 819996 + ... + 820021.

It is an arithmetic number, because the mean of its divisors is an integer number (5740063).

Almost surely, 2^21320221 is an apocalyptic number.

It is an amenable number.

21320221 is a deficient number, since it is larger than the sum of its proper divisors (1640031).

21320221 is a wasteful number, since it uses less digits than its factorization.

21320221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1640030.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21320221 is about 4617.3824836156. The cubic root of 21320221 is about 277.2876756936.

Adding to 21320221 its reverse (12202312), we get a palindrome (33522533).

The spelling of 21320221 in words is "twenty-one million, three hundred twenty thousand, two hundred twenty-one".