Then the number must be between 18² = 324 and 19² = 361. But is that what you want to know?
Answer: 
Step-by-step explanation:
Given
Vertex of the parabola 
Focus of the parabola 
As the x coordinate of vertex and focus is same and focus lie below the vertex, therefore the parabola is the type of

distance between Vertex and focus is 1 unit

Parabola becomes

I think to be a function is when you have to groups of something or if it's an number it can be an even number or an odd number you just have to find out what it is.