In excel, can I select cells in a random fashion using the CTRL key and a left click on the mouse and then have the sum of those cells placed in another cell?

Typically, I select a sequence of cells, like a1-a5 and press autosum and it puts the sum in a6, or a1-e1 and it puts the sum in f6. These cells are seqeuential in nature.

Instead of sitting on a6 and writing the formula a1+a2+a3+a4+a5.