Note: Plotting just 2 points will give you a straight line only. To see any curvature in a date set, you must plot more than 2 points and the x values must span the proper region.
I think Excel, Numbers or Google Sheets would be your best bet. You can define an x range of values in one column and then calculate the y values. Both Excel and Numbers have charting/plotting capabilities. Be sure to select "scatter plot" as your choice for chart type. You can then plot the x and y data you generated. You can choose bar chart if that is what you want. Below is an image of your result using Google Sheets. If you change the x, y or y2 values the chart will update to reflect the new values. The image won't update though.
There are other plotting apps for the Mac. The Mac comes with Grapher which is good for charting functions. There is also Magic Plot, and Veusz. These are probably overkill for what you want which is why I recommended a spreadsheet package.