a(1) = 4; then alternately add -4 and multiply by -2.

Terms

a(0) =4a(1) =0a(2) =0a(3) =-4a(4) =8a(5) =4a(6) =-8a(7) =-12a(8) =24a(9) =20a(10) =-40a(11) =-44a(12) =88a(13) =84a(14) =-168a(15) =-172a(16) =344a(17) =340a(18) =-680a(19) =-684a(20) =1368a(21) =1364a(22) =-2728a(23) =-2732a(24) =5464a(25) =5460a(26) =-10920a(27) =-10924a(28) =21848a(29) =21844