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

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =14a(5) =27a(6) =49a(7) =86a(8) =147a(9) =247a(10) =410a(11) =675a(12) =1105a(13) =1802a(14) =2931a(15) =4759a(16) =7718a(17) =12507a(18) =20257a(19) =32798a(20) =53091a(21) =85927a(22) =139058a(23) =225027a(24) =364129a(25) =589202a(26) =953379a(27) =1542631a(28) =2496062a(29) =4038747