17997991 has 4 divisors (see below), whose sum is σ = 19634184. Its totient is φ = 16361800.

The previous prime is 17997977. The next prime is 17998027. The reversal of 17997991 is 19979971.

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 17997991 - 2¹⁵ = 17965223 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 (17997191) 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, 818080 + ... + 818101.

It is an arithmetic number, because the mean of its divisors is an integer number (4908546).

Almost surely, 2^17997991 is an apocalyptic number.

17997991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

17997991 is a deficient number, since it is larger than the sum of its proper divisors (1636193).

17997991 is a wasteful number, since it uses less digits than its factorization.

17997991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1636192.

The product of its digits is 321489, while the sum is 52.

The square root of 17997991 is about 4242.4039175920. The cubic root of 17997991 is about 262.0643889295.

The spelling of 17997991 in words is "seventeen million, nine hundred ninety-seven thousand, nine hundred ninety-one".