a(n) = a(n-1) - a(n-2) + 3*a(n-3) with a(0) = 1, a(1) = 2 and a(2) = 4.

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =7a(5) =14a(6) =22a(7) =29a(8) =49a(9) =86a(10) =124a(11) =185a(12) =319a(13) =506a(14) =742a(15) =1193a(16) =1969a(17) =3002a(18) =4612a(19) =7517a(20) =11911a(21) =18230a(22) =28870a(23) =46373a(24) =72193a(25) =112430a(26) =179356a(27) =283505a(28) =441439a(29) =696002