18999809 has 4 divisors (see below), whose sum is σ = 19213380. Its totient is φ = 18786240.

The previous prime is 18999787. The next prime is 18999821. The reversal of 18999809 is 90899981.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7924225 + 11075584 = 2815^2 + 3328^2 .

It is a cyclic number.

It is not a de Polignac number, because 18999809 - 2²⁰ = 17951233 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18999839) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106652 + ... + 106829.

It is an arithmetic number, because the mean of its divisors is an integer number (4803345).

Almost surely, 2^18999809 is an apocalyptic number.

It is an amenable number.

18999809 is a deficient number, since it is larger than the sum of its proper divisors (213571).

18999809 is an equidigital number, since it uses as much as digits as its factorization.

18999809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213570.

The product of its (nonzero) digits is 419904, while the sum is 53.

The square root of 18999809 is about 4358.8770342830. The cubic root of 18999809 is about 266.8392707206.

The spelling of 18999809 in words is "eighteen million, nine hundred ninety-nine thousand, eight hundred nine".