18172009 has 4 divisors (see below), whose sum is σ = 18798660. Its totient is φ = 17545360.

The previous prime is 18171991. The next prime is 18172019. The reversal of 18172009 is 90027181.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90027181 = 3691 ⋅24391.

It can be written as a sum of positive squares in 2 ways, for example, as 6969600 + 11202409 = 2640^2 + 3347^2 .

It is a cyclic number.

It is not a de Polignac number, because 18172009 - 2⁵ = 18171977 is a prime.

It is a super-2 number, since 2×18172009² = 660443822192162, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18172019) 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, 313282 + ... + 313339.

It is an arithmetic number, because the mean of its divisors is an integer number (4699665).

Almost surely, 2^18172009 is an apocalyptic number.

It is an amenable number.

18172009 is a deficient number, since it is larger than the sum of its proper divisors (626651).

18172009 is an equidigital number, since it uses as much as digits as its factorization.

18172009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 626650.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 18172009 is about 4262.8639434071. The cubic root of 18172009 is about 262.9062926675.

The spelling of 18172009 in words is "eighteen million, one hundred seventy-two thousand, nine".