Geometric progression is a sequence of number where each turn is found by multiplying a constant number (GP). Example: a1=5 r=2, n=7: 5, 10, 20, 40, 80, 160, 320 This is finite. For finite terms, its n sigma i=0 ar^i, for infinite, n=infinity. The sigma notations means to sum up all result values when i=0 i=1... all the way to i=n.