18987809 has 4 divisors (see below), whose sum is σ = 19001220. Its totient is φ = 18974400.

The previous prime is 18987803. The next prime is 18987853. The reversal of 18987809 is 90878981.

It is a happy number.

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 15366400 + 3621409 = 3920^2 + 1903^2 .

It is a cyclic number.

It is not a de Polignac number, because 18987809 - 2¹⁶ = 18922273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18987803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4292 + ... + 7509.

It is an arithmetic number, because the mean of its divisors is an integer number (4750305).

Almost surely, 2^18987809 is an apocalyptic number.

It is an amenable number.

18987809 is a deficient number, since it is larger than the sum of its proper divisors (13411).

18987809 is a wasteful number, since it uses less digits than its factorization.

18987809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13410.

The product of its (nonzero) digits is 290304, while the sum is 50.

The square root of 18987809 is about 4357.5003155479. The cubic root of 18987809 is about 266.7830816362.

The spelling of 18987809 in words is "eighteen million, nine hundred eighty-seven thousand, eight hundred nine".