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

Terms

a(0) =4a(1) =4a(2) =5a(3) =8a(4) =12a(5) =21a(6) =36a(7) =64a(8) =113a(9) =204a(10) =372a(11) =682a(12) =1260a(13) =2340a(14) =4369a(15) =8192a(16) =15420a(17) =29127a(18) =55188a(19) =104857a(20) =199728a(21) =381300a(22) =729444a(23) =1398101a(24) =2684354a(25) =5162220a(26) =9942053a(27) =19173961a(28) =37025580a(29) =71582788