18008381 has 4 divisors (see below), whose sum is σ = 18495132. Its totient is φ = 17521632.

The previous prime is 18008377. The next prime is 18008383. The reversal of 18008381 is 18380081.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18380081 = 101 ⋅181981.

It can be written as a sum of positive squares in 2 ways, for example, as 8797156 + 9211225 = 2966^2 + 3035^2 .

It is a cyclic number.

It is not a de Polignac number, because 18008381 - 2² = 18008377 is a prime.

It is a super-2 number, since 2×18008381² = 648603572482322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18008383) 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, 243320 + ... + 243393.

It is an arithmetic number, because the mean of its divisors is an integer number (4623783).

Almost surely, 2^18008381 is an apocalyptic number.

It is an amenable number.

18008381 is a deficient number, since it is larger than the sum of its proper divisors (486751).

18008381 is an equidigital number, since it uses as much as digits as its factorization.

18008381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 486750.

The product of its (nonzero) digits is 1536, while the sum is 29.

The square root of 18008381 is about 4243.6282824960. The cubic root of 18008381 is about 262.1148079867.

The spelling of 18008381 in words is "eighteen million, eight thousand, three hundred eighty-one".