For fixed z and a=2, b>=a
For fixed z and a=2, b=7/3
For fixed z and a=2, b=8/3
For fixed z and a=2, b=10/3
For fixed z and a=2, b=11/3
For fixed z and a=2, b=13/3
For fixed z and a=2, b=14/3
For fixed z and a=2, b=16/3
For fixed z and a=2, b=17/3