18997591 has 4 divisors (see below), whose sum is σ = 19006632. Its totient is φ = 18988552.

The previous prime is 18997571. The next prime is 18997603. The reversal of 18997591 is 19579981.

It is a happy number.

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 18997591 - 2¹⁵ = 18964823 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 (18997571) 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, 465 + ... + 6181.

It is an arithmetic number, because the mean of its divisors is an integer number (4751658).

Almost surely, 2^18997591 is an apocalyptic number.

18997591 is a deficient number, since it is larger than the sum of its proper divisors (9041).

18997591 is an equidigital number, since it uses as much as digits as its factorization.

18997591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9040.

The product of its digits is 204120, while the sum is 49.

The square root of 18997591 is about 4358.6226035297. The cubic root of 18997591 is about 266.8288868875.

The spelling of 18997591 in words is "eighteen million, nine hundred ninety-seven thousand, five hundred ninety-one".