20666209 has 2 divisors, whose sum is σ = 20666210. Its totient is φ = 20666208.

The previous prime is 20666201. The next prime is 20666221. The reversal of 20666209 is 90266602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18835600 + 1830609 = 4340^2 + 1353^2 .

It is a cyclic number.

It is not a de Polignac number, because 20666209 - 2³ = 20666201 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20666201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10333104 + 10333105.

It is an arithmetic number, because the mean of its divisors is an integer number (10333105).

Almost surely, 2^20666209 is an apocalyptic number.

It is an amenable number.

20666209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20666209 is an equidigital number, since it uses as much as digits as its factorization.

20666209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 20666209 is about 4546.0102287610. The cubic root of 20666209 is about 274.4228512803.

The spelling of 20666209 in words is "twenty million, six hundred sixty-six thousand, two hundred nine".