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

Terms

a(0) =4a(1) =1a(2) =-1a(3) =1a(4) =7a(5) =6a(6) =-1a(7) =1a(8) =15a(9) =19a(10) =4a(11) =1a(12) =31a(13) =53a(14) =27a(15) =6a(16) =63a(17) =137a(18) =107a(19) =39a(20) =132a(21) =337a(22) =351a(23) =185a(24) =303a(25) =806a(26) =1039a(27) =721a(28) =791a(29) =1915