18055991 has 4 divisors (see below), whose sum is σ = 18065952. Its totient is φ = 18046032.

The previous prime is 18055927. The next prime is 18055993. The reversal of 18055991 is 19955081.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 18055991 - 2⁶ = 18055927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18055993) 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, 1406 + ... + 6171.

It is an arithmetic number, because the mean of its divisors is an integer number (4516488).

Almost surely, 2^18055991 is an apocalyptic number.

18055991 is a deficient number, since it is larger than the sum of its proper divisors (9961).

18055991 is an equidigital number, since it uses as much as digits as its factorization.

18055991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9960.

The product of its (nonzero) digits is 16200, while the sum is 38.

The square root of 18055991 is about 4249.2341662940. The cubic root of 18055991 is about 262.3455950608.

The spelling of 18055991 in words is "eighteen million, fifty-five thousand, nine hundred ninety-one".