Would putting several small propellers on a wing be efficient?
It would provide pretty good STOL performance at low speed because there is a significant increase in lift with the wing in the slipstream of a propeller, especially with flaps down.  One of the biggest differences between a jet and a turboprop while flying a landing approach is that power settings have a direct effect on sink rate with a turboprop where a quarter or a third of the wing span is in the propeller slipstream; not so much on a jet.

Then when you speed up, the inefficiency of all those draggy nacelles and relatively inefficient smaller propellers, the weight, the maintenance nightmare, the fuel burn.  Yikes.  That's why it's not done.

There's a reason that airplanes are all built to a few near-universal configurations.  They are the arrangements that hit a sweet spot, in the balance of compromises game, for the airplane's mission, and they are timeless until some major new paradigm comes along.  That's not one of them.