I'm confused what I am doing wrong. I have to "create a table of values and an associated graph that are decreasing and concave down."?

Hello I am currently working on a problem my prof. assigned and I'm confused what I am doing wrong.
I have to "create a table of values and an associated graph that are decreasing and concave down." How do I find the missing ? in the y's?
x y
1 49
2 ?
3 43
4 37
5 ?
6 19
0