The question Astronomical ABCD…! suggests a corollary for SXSE.
I'm looking for one example of a rocket with $n$ first-stage engines, for each $n$ for which you can think of an example for. It should be at least built, or very seriously proposed and investigated at a minimum.
I'll start off with some suggestions, items of recent popularity to get the ball rolling, but you don't have to use them.
Let's first try without jumping immediately to vehicles with variable strap-on number options, and see how that goes?