a(n) = 2^n*tetranacci(n) or (2^n)*A001648(n).

Terms

a(0) =2a(1) =12a(2) =56a(3) =240a(4) =832a(5) =3264a(6) =12672a(7) =48896a(8) =187904a(9) =724992a(10) =2795520a(11) =10776576a(12) =41541632a(13) =160153600a(14) =617414656a(15) =2380201984a(16) =9175957504a(17) =35374497792a(18) =136373075968a(19) =525735034880