Powers of -3: a(n) = (-3)^n.

Terms

a(0) =1a(1) =-3a(2) =9a(3) =-27a(4) =81a(5) =-243a(6) =729a(7) =-2187a(8) =6561a(9) =-19683a(10) =59049a(11) =-177147a(12) =531441a(13) =-1594323a(14) =4782969a(15) =-14348907a(16) =43046721a(17) =-129140163a(18) =387420489a(19) =-1162261467a(20) =3486784401a(21) =-10460353203a(22) =31381059609a(23) =-94143178827a(24) =282429536481a(25) =-847288609443