18991171 has 2 divisors, whose sum is σ = 18991172. Its totient is φ = 18991170.

The previous prime is 18991163. The next prime is 18991177. The reversal of 18991171 is 17119981.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 18991171 - 2³ = 18991163 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18991171.

It is not a weakly prime, because it can be changed into another prime (18991177) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9495585 + 9495586.

It is an arithmetic number, because the mean of its divisors is an integer number (9495586).

Almost surely, 2^18991171 is an apocalyptic number.

18991171 is a deficient number, since it is larger than the sum of its proper divisors (1).

18991171 is an equidigital number, since it uses as much as digits as its factorization.

18991171 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4536, while the sum is 37.

The square root of 18991171 is about 4357.8860701033. The cubic root of 18991171 is about 266.7988263313.

The spelling of 18991171 in words is "eighteen million, nine hundred ninety-one thousand, one hundred seventy-one".