Can anyone please help me recall this brain teaser?

I read this in the 1980’s from an issue of Reader’s Digest. I’m suppose to tell you that I could read your mind and to prove it, I would ask you to do all these in your head. Pick any two numbers between ___ and ___. Add this number to the number that follows it numerically and then multiply it by…and so on and so forth.

In the end you will have a number in your mind. Then I’m suppose to tell you to think of the corresponding letter of this number in the alphabet. I would then ask you to think of an animal whose name starts with the letter. I would then guess the right animal!

This brain teaser is rigged of course. It was made to always come up with that number and of course, the same letter, so guessing which animal is easy. I remember that most people I’ve done this with were so surprised that I guessed right so I would love to be able to do it again but I just can’t recall the exact questions. Darn.