18191891 has 4 divisors (see below), whose sum is σ = 18200784. Its totient is φ = 18183000.

The previous prime is 18191869. The next prime is 18191893. The reversal of 18191891 is 19819181.

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 a de Polignac number, because none of the positive numbers 2^k-18191891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18191893) 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, 341 + ... + 6041.

It is an arithmetic number, because the mean of its divisors is an integer number (4550196).

Almost surely, 2^18191891 is an apocalyptic number.

18191891 is a deficient number, since it is larger than the sum of its proper divisors (8893).

18191891 is an equidigital number, since it uses as much as digits as its factorization.

18191891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8892.

The product of its digits is 5184, while the sum is 38.

The square root of 18191891 is about 4265.1953061964. The cubic root of 18191891 is about 263.0021396694.

The spelling of 18191891 in words is "eighteen million, one hundred ninety-one thousand, eight hundred ninety-one".