git diff two sequential commits shortcut?

Question

I'd like to define a shortcut "git diffn" with this behavior:

git diffn := git diff HEAD HEAD~1
git diffn 1 := git diff HEAD~1 HEAD~2
git diffn 2 := git diff HEAD~2 HEAD~3
...

First one is no problem, but I don't know to to make the rest.

Answer 1

What about:

git show - shows the last commit

git show HEAD~1 - shows the last but one commit

git show <COMMIT SHA> - shows you any commit

git whatchanged - shows you which files changed against the git log