Massachusetts Institute of Technology: Srini Devadas and Eric Lehman's "Notes for Recitation 2"
Read the recitation on pages 1 - 5. These give more examples of proof techniques for numbers.
Click https://s3.amazonaws.com/saylordotorg-resources/wwwresources/site/wp-content/uploads/2011/09/CS202-Case-Analysis.pdf link to open resource.