> suppose you have a sequence like a_n = n^3: 0, 1, 8, 27, ... > > Then I call the sequence 3n^2 + 3n + 1 the "difference sequence" or > the "sequence of differences" -- is this generally accepted > terminology? And I denote the terms Da_n. Is there a more standard > way to write that? I have seen both D and \Delta (uppercase Greek delta, triangle) in the literature. ralf