18681891 has 4 divisors (see below), whose sum is σ = 24909192. Its totient is φ = 12454592.

The previous prime is 18681863. The next prime is 18681899. The reversal of 18681891 is 19818681.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18681891 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18681899) 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, 3113646 + ... + 3113651.

It is an arithmetic number, because the mean of its divisors is an integer number (6227298).

Almost surely, 2^18681891 is an apocalyptic number.

18681891 is a deficient number, since it is larger than the sum of its proper divisors (6227301).

18681891 is an equidigital number, since it uses as much as digits as its factorization.

18681891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6227300.

The product of its digits is 27648, while the sum is 42.

The square root of 18681891 is about 4322.2553140693. The cubic root of 18681891 is about 265.3425781832.

The spelling of 18681891 in words is "eighteen million, six hundred eighty-one thousand, eight hundred ninety-one".