21102209 has 2 divisors, whose sum is σ = 21102210. Its totient is φ = 21102208.

The previous prime is 21102199. The next prime is 21102239. The reversal of 21102209 is 90220112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11242609 + 9859600 = 3353^2 + 3140^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21102209 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21102239) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10551104 + 10551105.

It is an arithmetic number, because the mean of its divisors is an integer number (10551105).

Almost surely, 2^21102209 is an apocalyptic number.

It is an amenable number.

21102209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21102209 is an equidigital number, since it uses as much as digits as its factorization.

21102209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 21102209 is about 4593.7140746895. The cubic root of 21102209 is about 276.3392916516.

The spelling of 21102209 in words is "twenty-one million, one hundred two thousand, two hundred nine".