21309221 has 2 divisors, whose sum is σ = 21309222. Its totient is φ = 21309220.

The previous prime is 21309193. The next prime is 21309257. The reversal of 21309221 is 12290312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 57121 = 4610^2 + 239^2 .

It is a cyclic number.

It is not a de Polignac number, because 21309221 - 2¹⁴ = 21292837 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21309193 and 21309202.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21302221) 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 as a sum of consecutive naturals, namely, 10654610 + 10654611.

It is an arithmetic number, because the mean of its divisors is an integer number (10654611).

Almost surely, 2^21309221 is an apocalyptic number.

It is an amenable number.

21309221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21309221 is an equidigital number, since it uses as much as digits as its factorization.

21309221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 21309221 is about 4616.1911788833. The cubic root of 21309221 is about 277.2399793594.

Adding to 21309221 its reverse (12290312), we get a palindrome (33599533).

The spelling of 21309221 in words is "twenty-one million, three hundred nine thousand, two hundred twenty-one".