20855909 has 2 divisors, whose sum is σ = 20855910. Its totient is φ = 20855908.

The previous prime is 20855897. The next prime is 20855911. The reversal of 20855909 is 90955802.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12271009 + 8584900 = 3503^2 + 2930^2 .

It is a cyclic number.

It is not a de Polignac number, because 20855909 - 2⁴ = 20855893 is a prime.

It is a Sophie Germain prime.

Together with 20855911, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20855929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10427954 + 10427955.

It is an arithmetic number, because the mean of its divisors is an integer number (10427955).

Almost surely, 2^20855909 is an apocalyptic number.

It is an amenable number.

20855909 is a deficient number, since it is larger than the sum of its proper divisors (1).

20855909 is an equidigital number, since it uses as much as digits as its factorization.

20855909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32400, while the sum is 38.

The square root of 20855909 is about 4566.8270166495. The cubic root of 20855909 is about 275.2599591403.

The spelling of 20855909 in words is "twenty million, eight hundred fifty-five thousand, nine hundred nine".