18199981 has 4 divisors (see below), whose sum is σ = 18215932. Its totient is φ = 18184032.

The previous prime is 18199963. The next prime is 18199999. The reversal of 18199981 is 18999181.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (18199963) and next prime (18199999).

It can be written as a sum of positive squares in 2 ways, for example, as 13616100 + 4583881 = 3690^2 + 2141^2 .

It is a cyclic number.

It is not a de Polignac number, because 18199981 - 2⁵ = 18199949 is a prime.

It is a super-2 number, since 2×18199981² = 662478616800722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18199931) 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, 6120 + ... + 8593.

It is an arithmetic number, because the mean of its divisors is an integer number (4553983).

Almost surely, 2^18199981 is an apocalyptic number.

It is an amenable number.

18199981 is a deficient number, since it is larger than the sum of its proper divisors (15951).

18199981 is a wasteful number, since it uses less digits than its factorization.

18199981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15950.

The product of its digits is 46656, while the sum is 46.

The square root of 18199981 is about 4266.1435747054. The cubic root of 18199981 is about 263.0411198940.

Subtracting from 18199981 its product of digits (46656), we obtain a triangular number (18153325 = T₆₀₂₅).

The spelling of 18199981 in words is "eighteen million, one hundred ninety-nine thousand, nine hundred eighty-one".