A few things. Instead of "a=push!(a,(2*((4*g*g)-g)))" you can just do push!(a, ...) and that will modify the existing a so that is has the last element appended. There is no need to assign the result to a again.
I think the way you read a user input and then use parse to get the Int for it is perfectly fine. The rest is also fine to me. A common workflow in Julia is that you create your own types like and write function that work on them (see http://docs.julialang.org/en/release-0.4/manual/types/). If you want to learn to write good Julia that is something that would be good looking into how to do. Good luck and continue to ask questions. There is also quite a lot of material online on Julia that you can learn that you can find by some simple googling.
