I wrote it kinda weird.
(c+1)/2 = ((a-1)/2)(b-1) + (a+b)/2
Multiply each thing by 2
c+1 = 2((a-1)/2) * 2(b-1) + (a+b)
Simplify
c+1 = (a-1)*(2(b-1)) + a + b
Which is what I meant by
c+1 = (a-1)2(b-1) + a+b
which is typed out wrong. The logic's still there.
If you know what to do, feel free to do it. I don't think I really understand how you'd do that but it could be useful. It's an avenue I don't think any of us have explored, so I'm sure there's a lot to discover. Some examples of points would be (e,n) = (30,5) and (30,257) for a=13, b=43, and then (e,n) = (7,4) and (7,88) for a=7, b=29.