20897909 has 2 divisors, whose sum is σ = 20897910. Its totient is φ = 20897908.

The previous prime is 20897873. The next prime is 20897917. The reversal of 20897909 is 90979802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20729809 + 168100 = 4553^2 + 410^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20897909 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20897909.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20897969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10448954 + 10448955.

It is an arithmetic number, because the mean of its divisors is an integer number (10448955).

Almost surely, 2^20897909 is an apocalyptic number.

It is an amenable number.

20897909 is a deficient number, since it is larger than the sum of its proper divisors (1).

20897909 is an equidigital number, since it uses as much as digits as its factorization.

20897909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 81648, while the sum is 44.

The square root of 20897909 is about 4571.4230825860. The cubic root of 20897909 is about 275.4446097099. Note that the first 3 decimals are identical.

The spelling of 20897909 in words is "twenty million, eight hundred ninety-seven thousand, nine hundred nine".