a(n) = 3*a(n-1) - 4*a(n-3), with a(0)=1, a(1)=2, a(2)=4, a(3)=7.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =13a(5) =23a(6) =41a(7) =71a(8) =121a(9) =199a(10) =313a(11) =455a(12) =569a(13) =455a(14) =-455a(15) =-3641a(16) =-12743a(17) =-36409a(18) =-94663a(19) =-233017a(20) =-553415a(21) =-1281593a(22) =-2912711a(23) =-6524473a(24) =-14447047a(25) =-31690297a(26) =-68972999a(27) =-149130809a(28) =-320631239a(29) =-686001721