a(n) = 2*a(n-1) + a(n-2), with a(0)= -1, a(1)= 3.

Terms

a(0) =-1a(1) =3a(2) =5a(3) =13a(4) =31a(5) =75a(6) =181a(7) =437a(8) =1055a(9) =2547a(10) =6149a(11) =14845a(12) =35839a(13) =86523a(14) =208885a(15) =504293a(16) =1217471a(17) =2939235a(18) =7095941a(19) =17131117a(20) =41358175a(21) =99847467a(22) =241053109a(23) =581953685a(24) =1404960479a(25) =3391874643a(26) =8188709765a(27) =19769294173a(28) =47727298111a(29) =115223890395