a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) for n > 4, with first terms 1, 2, 4, 7.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =12a(5) =22a(6) =44a(7) =92a(8) =192a(9) =392a(10) =784a(11) =1552a(12) =3072a(13) =6112a(14) =12224a(15) =24512a(16) =49152a(17) =98432a(18) =196864a(19) =393472a(20) =786432a(21) =1572352a(22) =3144704a(23) =6290432a(24) =12582912a(25) =25167872a(26) =50335744a(27) =100667392a(28) =201326592a(29) =402644992