#### Why is the number 9 excluded?

The number 9 has been excluded to ensure that all sets of numbers (evens/single digits/primes/etc) have eight numbers, which is exactly half of the total number of numbers. In other words, each attribute, e.g., evens and odds, divides the 16 total numbers into two equal sets.

#### What is a prime number? A composite number?

A prime number is a number that can only be divided by itself and 1. The prime numbers are 1*, 2, 3, 5, 7, 11, 13, and 17. The composite numbers are 4, 6, 8, 10, 12, 14, 15, and 16.

*Strictly speaking, the number 1 is neither prime nor composite. But for the purposes of this game, it will be considered prime.

#### Which numbers are the “middles” and which numbers are the “edges”?

The “middles” consist of the numbers 5 ~ 13 (excluding 9) and the “edges” consist of all the rest of the numbers (1 ~ 4 and 14 ~ 17). A good way to remember them is that every set of numbers, whether it be evens, single digits, primes, middles, or edges, consists of eight numbers.

#### How do I differentiate between the numbers I placed and the numbers my opponent placed?

You do not need to. Number Cortex is an impartial game. Thus the board looks exactly the same to you and your opponent. The only difference is that while you are making your turn, your opponent is not. Hence, some people call Number Cortex a “game of timing.”

#### I keep accidentally tapping the numbers in the scroller. Is there anything I can do about this?

Yes. Go to the “Options” screen, and turn on the “double tap to choose” function. Although you will now have to double tap a number to choose it, you will have a much lower chance of accidentally choosing the wrong number.

#### Why am I only allowed ONE adjustment of a number placement?

The feature which allows you to adjust the placement of a number was created to help you in case you made a mistake while dragging and dropping. It is not meant to be used as a strategic tool.

#### Is there any difference between level 17 and level 18?

Yes. In level 18, you always go first. Does this matter? See the question below.

#### Is it better to go first?

In short, it does not really make a difference unless you are on a difficult level. See the following post for a most detailed answer.