18531809 has 4 divisors (see below), whose sum is σ = 18650004. Its totient is φ = 18413616.

The previous prime is 18531803. The next prime is 18531827. The reversal of 18531809 is 90813581.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90813581 = 79 ⋅1149539.

It can be written as a sum of positive squares in 2 ways, for example, as 6477025 + 12054784 = 2545^2 + 3472^2 .

It is a cyclic number.

It is not a de Polignac number, because 18531809 - 2⁸ = 18531553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18531803) 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, 58862 + ... + 59175.

It is an arithmetic number, because the mean of its divisors is an integer number (4662501).

Almost surely, 2^18531809 is an apocalyptic number.

It is an amenable number.

18531809 is a deficient number, since it is larger than the sum of its proper divisors (118195).

18531809 is a wasteful number, since it uses less digits than its factorization.

18531809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118194.

The product of its (nonzero) digits is 8640, while the sum is 35.

The square root of 18531809 is about 4304.8587665567. The cubic root of 18531809 is about 264.6301188323.

The spelling of 18531809 in words is "eighteen million, five hundred thirty-one thousand, eight hundred nine".