20187809 has 2 divisors, whose sum is σ = 20187810. Its totient is φ = 20187808.

The previous prime is 20187803. The next prime is 20187821. The reversal of 20187809 is 90878102.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18490000 + 1697809 = 4300^2 + 1303^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20187809 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20187803) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10093904 + 10093905.

It is an arithmetic number, because the mean of its divisors is an integer number (10093905).

Almost surely, 2^20187809 is an apocalyptic number.

It is an amenable number.

20187809 is a deficient number, since it is larger than the sum of its proper divisors (1).

20187809 is an equidigital number, since it uses as much as digits as its factorization.

20187809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8064, while the sum is 35.

The square root of 20187809 is about 4493.0845752111. The cubic root of 20187809 is about 272.2887693354.

The spelling of 20187809 in words is "twenty million, one hundred eighty-seven thousand, eight hundred nine".