18990809 has 2 divisors, whose sum is σ = 18990810. Its totient is φ = 18990808.

The previous prime is 18990793. The next prime is 18990827. The reversal of 18990809 is 90809981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14137600 + 4853209 = 3760^2 + 2203^2 .

It is an emirp because it is prime and its reverse (90809981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18990809 - 2⁴ = 18990793 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 18990809.

It is not a weakly prime, because it can be changed into another prime (18990869) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9495404 + 9495405.

It is an arithmetic number, because the mean of its divisors is an integer number (9495405).

Almost surely, 2^18990809 is an apocalyptic number.

It is an amenable number.

18990809 is a deficient number, since it is larger than the sum of its proper divisors (1).

18990809 is an equidigital number, since it uses as much as digits as its factorization.

18990809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 46656, while the sum is 44.

The square root of 18990809 is about 4357.8445360063. The cubic root of 18990809 is about 266.7971311262.

The spelling of 18990809 in words is "eighteen million, nine hundred ninety thousand, eight hundred nine".