a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3), n > 3; a(0) = 1, a(1) = 4, a(2) = 12, a(3) = 32.

Terms

a(0) =1a(1) =4a(2) =12a(3) =32a(4) =72a(5) =144a(6) =272a(7) =512a(8) =992a(9) =1984a(10) =4032a(11) =8192a(12) =16512a(13) =33024a(14) =65792a(15) =131072a(16) =261632a(17) =523264a(18) =1047552a(19) =2097152a(20) =4196352a(21) =8392704a(22) =16781312a(23) =33554432a(24) =67100672a(25) =134201344a(26) =268419072a(27) =536870912a(28) =1073774592a(29) =2147549184