There are an infinite amount of answers to that, but 1.85 is the number that is halfway between them.
The number 19 it is between 18 and 20 and is a Prime Number.
The single number directly between those two numbers is 18.
18 is a natural number following 17 and preecending 19 18 is a natural number following 17 and preecending 19 18 is a natural number following 17 and preecending 19 you become an adult
19-18 leaves 1 second.
18 falls between 17 and 19.
The number 19 it is between 18 and 20 and is a Prime Number.
The single number directly between those two numbers is 18.
18 is a natural number following 17 and preecending 19 18 is a natural number following 17 and preecending 19 18 is a natural number following 17 and preecending 19 you become an adult
The first prime number after 18 is 19.
19-18 leaves 1 second.
18 falls between 17 and 19.
19 is prime.
4.01234567891011121314... keep appending the next counting number on the end {15, 16, 17, 18, 19, 20, ...} and you will have an irrational number between 4 and 5.
18.
19 YES, 19 is prime because 2,3,4,5,6,7,8,9,do not go in to 19. I stop at nine because 18 is one under 19 and 9 x 2=18. The only factors of 19 are 1 and itself, making it a prime number.
19 goes there, of course, unless there is more to this riddle than is so obvious!
The answer is 18 since the atomic number of Potassium is 19. Mathematically, = 19 - 1 = 18