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

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =30a(5) =121a(6) =493a(7) =2011a(8) =8204a(9) =33469a(10) =136540a(11) =557028a(12) =2272449a(13) =9270673a(14) =37820597a(15) =154292742a(16) =629451995a(17) =2567909604a(18) =10476032782a(19) =42737977489a(20) =174353665921a(21) =711292452431