18987791 has 2 divisors, whose sum is σ = 18987792. Its totient is φ = 18987790.

The previous prime is 18987769. The next prime is 18987803. The reversal of 18987791 is 19778981.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 18987791 - 2¹⁰ = 18986767 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18987191) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9493895 + 9493896.

It is an arithmetic number, because the mean of its divisors is an integer number (9493896).

Almost surely, 2^18987791 is an apocalyptic number.

18987791 is a deficient number, since it is larger than the sum of its proper divisors (1).

18987791 is an equidigital number, since it uses as much as digits as its factorization.

18987791 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 254016, while the sum is 50.

The square root of 18987791 is about 4357.4982501431. The cubic root of 18987791 is about 266.7829973348.

The spelling of 18987791 in words is "eighteen million, nine hundred eighty-seven thousand, seven hundred ninety-one".