a(n) = a(n-1) + 3*a(n-2) -2*a(n-3) - 2*a(n-4), where a(0) = 1, a(1) = 3, a(2) = 6, a(3) = 10.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =20a(5) =32a(6) =60a(7) =96a(8) =172a(9) =276a(10) =480a(11) =772a(12) =1316a(13) =2120a(14) =3564a(15) =5748a(16) =9568a(17) =15444a(18) =25524a(19) =41224a(20) =67772a(21) =109508a(22) =179328a(23) =289860a(24) =473284a(25) =765192a(26) =1246668a(27) =2015956a(28) =3279008a(29) =5303156