21215201209 has 2 divisors, whose sum is σ = 21215201210. Its totient is φ = 21215201208.

The previous prime is 21215201207. The next prime is 21215201237. The reversal of 21215201209 is 90210251212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19945347984 + 1269853225 = 141228^2 + 35635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215201209 - 2¹ = 21215201207 is a prime.

Together with 21215201207, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21215201207) 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, 10607600604 + 10607600605.

It is an arithmetic number, because the mean of its divisors is an integer number (10607600605).

Almost surely, 2^21215201209 is an apocalyptic number.

It is an amenable number.

21215201209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215201209 is an equidigital number, since it uses as much as digits as its factorization.

21215201209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 25.

The spelling of 21215201209 in words is "twenty-one billion, two hundred fifteen million, two hundred one thousand, two hundred nine".