a(n+3) = 3*a(n+2) + 2*a(n+1) - a(n).

Terms

a(0) =1a(1) =4a(2) =13a(3) =46a(4) =160a(5) =559a(6) =1951a(7) =6811a(8) =23776a(9) =82999a(10) =289738a(11) =1011436a(12) =3530785a(13) =12325489a(14) =43026601a(15) =150199996a(16) =524327701a(17) =1830356494a(18) =6389524888a(19) =22304959951a(20) =77863573135a(21) =271811114419a(22) =948855529576