Not sure about this but it looks like we subtract 1 from the first number then add 3 times the difference in the example (N) to get each subsequent number so the Z part is in 1:
10-1 = 9 and second value is 9 + 3*(15-10) = 24 and third is 24 * 3*18 = 78 and so on.
Sensitivity analysis is the study of how the uncertainty in the output of a mathematical model or system (numerical or otherwise) can be divided and allocated to different sources of uncertainty in its inputs.
