a(n) = a(n-1) + 2*a(n-2) + (-1)^n.

Terms

a(0) =1a(1) =1a(2) =4a(3) =5a(4) =14a(5) =23a(6) =52a(7) =97a(8) =202a(9) =395a(10) =800a(11) =1589a(12) =3190a(13) =6367a(14) =12748a(15) =25481a(16) =50978a(17) =101939a(18) =203896a(19) =407773a(20) =815566a(21) =1631111a(22) =3262244a(23) =6524465a(24) =13048954a(25) =26097883a(26) =52195792a(27) =104391557a(28) =208783142a(29) =417566255