Excellent alternate choices for Your Favorite Lenny:
Top to bottom, left to right: Bruce, Bernstein, Briscoe, daVinci, Smalls, Nimoy, Sheldon (last name Leonard)
Any of these or others could be Your Favorite Lenny; but My Favorite Lenny is still Leonhard Euler.
Let's start with the Euler characteristic, sometimes known as the Euler-Poincaré characteristic. (They didn't work together; Henri Poincaré shows up more than a century later and extends the work Euler did on this.)
Think of a cube. It has 6 faces, 8 corners (we will call them vertices) and 12 edges.
Consider a pyramid. It has 5 faces (including the base), 5 vertices and 8 edges.
The Euler characteristic says F + V = E + 2. This is true for any 3-d geometric shape with flat surfaces for faces, as long as there is no hole that goes through the shape; the technical term is polyhedron. For surfaces with holes (think of a donut, or drilling a rectangular tunnel through a cube that extends from one face to another), the formula changes to F + V = E + 2 + 2G, where G is the number of such holes, known as the genus of the solid.
You might say, "Hey, Matty Boy! What about a sphere? It has one face, no vertices and no edges. 1 + 0 = 0 + 2 is wrong! Ha, ha, ha!"
You're right, but the shape hasn't been properly Eulerized; we need at least 1 vertex, and if there are at least 2 vertices, then we need edges as well to create faces. Let's pick a point on the sphere and call that a vertex. 1 + 1 = 0 + 2.
Let's draw a Great Circle that goes through that point. (A Great Circle is the largest circle that can be drawn on a sphere, like the equator on Earth.) We now have 1 vertex and 1 edge, and the sphere now has 2 faces, call them north and south. 2 faces, 1 vertex, 1 edge. 2 + 1 = 1 + 2.
My Favorite Lenny.