a(n) = ceiling(2^(n+1)/n).

Terms

a(0) =4a(1) =4a(2) =6a(3) =8a(4) =13a(5) =22a(6) =37a(7) =64a(8) =114a(9) =205a(10) =373a(11) =683a(12) =1261a(13) =2341a(14) =4370a(15) =8192a(16) =15421a(17) =29128a(18) =55189a(19) =104858a(20) =199729a(21) =381301a(22) =729445a(23) =1398102a(24) =2684355a(25) =5162221a(26) =9942054a(27) =19173962a(28) =37025581a(29) =71582789