Hi Bison, --------- The first and the last letter are the same and go in the normal order: A, B, C...... the 2nd letter skipps 2 letters each time, so it is A, D, G, J, M, P...... etc.... The 3rd letter alters between A and Z...... A Z A Z A Z ..... etc..... So the answer of my friend ProfitBob is Perfect (as always - thumb up). ----- Best regards,