a(n) = -a(n-1) + 2*a(n-2), a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =0a(3) =4a(4) =-4a(5) =12a(6) =-20a(7) =44a(8) =-84a(9) =172a(10) =-340a(11) =684a(12) =-1364a(13) =2732a(14) =-5460a(15) =10924a(16) =-21844a(17) =43692a(18) =-87380a(19) =174764a(20) =-349524a(21) =699052a(22) =-1398100a(23) =2796204a(24) =-5592404a(25) =11184812a(26) =-22369620a(27) =44739244a(28) =-89478484a(29) =178956972