17998991 has 4 divisors (see below), whose sum is σ = 18041184. Its totient is φ = 17956800.

The previous prime is 17998973. The next prime is 17998993. The reversal of 17998991 is 19989971.

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

It is a cyclic number.

It is not a de Polignac number, because 17998991 - 2⁶ = 17998927 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 (17998993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20450 + ... + 21311.

It is an arithmetic number, because the mean of its divisors is an integer number (4510296).

Almost surely, 2^17998991 is an apocalyptic number.

17998991 is a deficient number, since it is larger than the sum of its proper divisors (42193).

17998991 is an equidigital number, since it uses as much as digits as its factorization.

17998991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42192.

The product of its digits is 367416, while the sum is 53.

The square root of 17998991 is about 4242.5217736625. The cubic root of 17998991 is about 262.0692424256.

The spelling of 17998991 in words is "seventeen million, nine hundred ninety-eight thousand, nine hundred ninety-one".