21068309 has 2 divisors, whose sum is σ = 21068310. Its totient is φ = 21068308.

The previous prime is 21068291. The next prime is 21068317. The reversal of 21068309 is 90386012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20160100 + 908209 = 4490^2 + 953^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21068309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21068339) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10534154 + 10534155.

It is an arithmetic number, because the mean of its divisors is an integer number (10534155).

Almost surely, 2^21068309 is an apocalyptic number.

It is an amenable number.

21068309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21068309 is an equidigital number, since it uses as much as digits as its factorization.

21068309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21068309 is about 4590.0227668281. The cubic root of 21068309 is about 276.1912357004.

The spelling of 21068309 in words is "twenty-one million, sixty-eight thousand, three hundred nine".