18131809 has 4 divisors (see below), whose sum is σ = 19198404. Its totient is φ = 17065216.

The previous prime is 18131803. The next prime is 18131819. The reversal of 18131809 is 90813181.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90813181 = 29 ⋅3131489.

It can be written as a sum of positive squares in 2 ways, for example, as 6250000 + 11881809 = 2500^2 + 3447^2 .

It is a cyclic number.

It is not a de Polignac number, because 18131809 - 2⁹ = 18131297 is a prime.

It is a super-2 number, since 2×18131809² = 657524995224962, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18131803) 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, 533272 + ... + 533305.

It is an arithmetic number, because the mean of its divisors is an integer number (4799601).

Almost surely, 2^18131809 is an apocalyptic number.

It is an amenable number.

18131809 is a deficient number, since it is larger than the sum of its proper divisors (1066595).

18131809 is a wasteful number, since it uses less digits than its factorization.

18131809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1066594.

The product of its (nonzero) digits is 1728, while the sum is 31.

The square root of 18131809 is about 4258.1461928872. The cubic root of 18131809 is about 262.7122830052.

The spelling of 18131809 in words is "eighteen million, one hundred thirty-one thousand, eight hundred nine".