17-22 Find a formula for the general te assuming that the pattern of the first few terms continues.17.{12,14,16,18,110,dots}18.{4,-1,14,-116,164,dots}19.{-3,2,-43,89,-1627,dots}20.{5,8,11,14,17,dots}21.{12,-43,94,-165,256,dots}22.{1,0,-1,0,1,0,-1,0,dots}