21323209 has 2 divisors, whose sum is σ = 21323210. Its totient is φ = 21323208.

The previous prime is 21323191. The next prime is 21323261. The reversal of 21323209 is 90232312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16605625 + 4717584 = 4075^2 + 2172^2 .

It is a cyclic number.

It is not a de Polignac number, because 21323209 - 2⁵ = 21323177 is a prime.

It is a plaindrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 21323209.

It is not a weakly prime, because it can be changed into another prime (21323509) 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 as a sum of consecutive naturals, namely, 10661604 + 10661605.

It is an arithmetic number, because the mean of its divisors is an integer number (10661605).

Almost surely, 2^21323209 is an apocalyptic number.

It is an amenable number.

21323209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21323209 is an equidigital number, since it uses as much as digits as its factorization.

21323209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 22.

The square root of 21323209 is about 4617.7060322199. The cubic root of 21323209 is about 277.3006289188.

The spelling of 21323209 in words is "twenty-one million, three hundred twenty-three thousand, two hundred nine".