20909209 has 2 divisors, whose sum is σ = 20909210. Its totient is φ = 20909208.

The previous prime is 20909183. The next prime is 20909281. The reversal of 20909209 is 90290902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13483584 + 7425625 = 3672^2 + 2725^2 .

It is a cyclic number.

It is not a de Polignac number, because 20909209 - 2⁷ = 20909081 is a prime.

It is not a weakly prime, because it can be changed into another prime (20969209) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10454604 + 10454605.

It is an arithmetic number, because the mean of its divisors is an integer number (10454605).

Almost surely, 2^20909209 is an apocalyptic number.

It is an amenable number.

20909209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20909209 is an equidigital number, since it uses as much as digits as its factorization.

20909209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 20909209 is about 4572.6588545397. The cubic root of 20909209 is about 275.4942472638.

The spelling of 20909209 in words is "twenty million, nine hundred nine thousand, two hundred nine".