21170209 has 2 divisors, whose sum is σ = 21170210. Its totient is φ = 21170208.

The previous prime is 21170207. The next prime is 21170213. The reversal of 21170209 is 90207112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17875984 + 3294225 = 4228^2 + 1815^2 .

It is a cyclic number.

It is not a de Polignac number, because 21170209 - 2¹ = 21170207 is a prime.

Together with 21170207, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21170209.

It is not a weakly prime, because it can be changed into another prime (21170207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585104 + 10585105.

It is an arithmetic number, because the mean of its divisors is an integer number (10585105).

Almost surely, 2^21170209 is an apocalyptic number.

It is an amenable number.

21170209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21170209 is an equidigital number, since it uses as much as digits as its factorization.

21170209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 252, while the sum is 22.

The square root of 21170209 is about 4601.1095401001. The cubic root of 21170209 is about 276.6357996886.

The spelling of 21170209 in words is "twenty-one million, one hundred seventy thousand, two hundred nine".