21212121209 has 2 divisors, whose sum is σ = 21212121210. Its totient is φ = 21212121208.

The previous prime is 21212121199. The next prime is 21212121283. The reversal of 21212121209 is 90212121212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16619077225 + 4593043984 = 128915^2 + 67772^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212121209 - 2¹⁶ = 21212055673 is a prime.

It is not a weakly prime, because it can be changed into another prime (21212121299) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606060604 + 10606060605.

It is an arithmetic number, because the mean of its divisors is an integer number (10606060605).

Almost surely, 2^21212121209 is an apocalyptic number.

It is an amenable number.

21212121209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212121209 is an equidigital number, since it uses as much as digits as its factorization.

21212121209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 23.

The spelling of 21212121209 in words is "twenty-one billion, two hundred twelve million, one hundred twenty-one thousand, two hundred nine".