a(n) = 4a(n-1) - 4a(n-2) + 3a(n-3) + a(n-4) - a(n-5).

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =42a(5) =128a(6) =389a(7) =1179a(8) =3572a(9) =10825a(10) =32810a(11) =99446a(12) =301412a(13) =913547a(14) =2768863a(15) =8392136a(16) =25435699a(17) =77092976a(18) =233660832a(19) =708201794a(20) =2146486339a(21) =6505777953a(22) =19718339694a(23) =59764246943a(24) =181139247400a(25) =549014312524