a(0) = 2, a(1) = 2; for n > 1, a(n) = a(n-1) + 2*a(n-2) + 3.

Terms

a(0) =2a(1) =2a(2) =9a(3) =16a(4) =37a(5) =72a(6) =149a(7) =296a(8) =597a(9) =1192a(10) =2389a(11) =4776a(12) =9557a(13) =19112a(14) =38229a(15) =76456a(16) =152917a(17) =305832a(18) =611669a(19) =1223336a(20) =2446677a(21) =4893352a(22) =9786709a(23) =19573416a(24) =39146837a(25) =78293672a(26) =156587349a(27) =313174696a(28) =626349397a(29) =1252698792