a(n) = 3*a(n-2) for n > 2; a(1) = 3, a(2) = -1.

Terms

a(0) =3a(1) =-1a(2) =9a(3) =-3a(4) =27a(5) =-9a(6) =81a(7) =-27a(8) =243a(9) =-81a(10) =729a(11) =-243a(12) =2187a(13) =-729a(14) =6561a(15) =-2187a(16) =19683a(17) =-6561a(18) =59049a(19) =-19683a(20) =177147a(21) =-59049a(22) =531441a(23) =-177147a(24) =1594323a(25) =-531441a(26) =4782969a(27) =-1594323a(28) =14348907a(29) =-4782969