If you look at the Y-values, you will discover that each one is one less than the corresponding term of this sequence: 2, 4, 8, 16, 32, 64, 128 which are the 1st, 2nd, 3rd, 4th, etc. powers of 2. So the X-th term of the given sequence is 1 less than 2X. So the equation you're looking for is: Y = 2X - 1 You just have to be observant and familiar with the various powers of small numbers to do problems like these. Edwin