a(0) = 1; a(1) = 2; a(n) = { a(n-1) + a(n-2) for n even, a(n-1) - a(n-2) for n odd }.

Terms

a(0) =1a(1) =2a(2) =3a(3) =1a(4) =4a(5) =3a(6) =7a(7) =4a(8) =11a(9) =7a(10) =18a(11) =11a(12) =29a(13) =18a(14) =47a(15) =29a(16) =76a(17) =47a(18) =123a(19) =76a(20) =199a(21) =123a(22) =322a(23) =199a(24) =521a(25) =322a(26) =843a(27) =521a(28) =1364a(29) =843