2106809 has 2 divisors, whose sum is σ = 2106810. Its totient is φ = 2106808.

The previous prime is 2106781. The next prime is 2106829. The reversal of 2106809 is 9086012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1210000 + 896809 = 1100^2 + 947^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2106809 is a prime.

It is a Chen prime.

It is an Ulam number.

It is not a weakly prime, because it can be changed into another prime (2106829) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1053404 + 1053405.

It is an arithmetic number, because the mean of its divisors is an integer number (1053405).

2^2106809 is an apocalyptic number.

It is an amenable number.

2106809 is a deficient number, since it is larger than the sum of its proper divisors (1).

2106809 is an equidigital number, since it uses as much as digits as its factorization.

2106809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 2106809 is about 1451.4851015426. The cubic root of 2106809 is about 128.1961713643.

The spelling of 2106809 in words is "two million, one hundred six thousand, eight hundred nine".