Can a number be both odd and even?
What does this tell you about where the ODD NUMBER and EVEN NUMBER
headings have to go?
Can you use this idea to position any of the other heading
If you have reached a stage where you have placed most of the
numbers but have a few that you cannot place, don't panic!
Could you swap one of the numbers that you can't place for a number
that is already on the grid?
You might be able to swap them and then find that the number you
have removed can be placed on one of the empty squares.
Don't forget: $1$ is not a prime number!
can be represented by a triangular array of