I have a lot of trouble trying to figure out the explcit forumla of a series of numbers. I can see the pattern in a recursion forumla, however. [tex] 2, -4, 8, -16, ...[/tex] Is a multiplication of [tex]-2[/tex] to the term before it. Which is cake to write in a recursion forumla. But what about an Explicit Formula? What techniques and ideas do you look for first? Are there any clues?