a(n) = floor(2^(n+2)/7).

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =18a(5) =36a(6) =73a(7) =146a(8) =292a(9) =585a(10) =1170a(11) =2340a(12) =4681a(13) =9362a(14) =18724a(15) =37449a(16) =74898a(17) =149796a(18) =299593a(19) =599186a(20) =1198372a(21) =2396745a(22) =4793490a(23) =9586980a(24) =19173961a(25) =38347922a(26) =76695844a(27) =153391689a(28) =306783378a(29) =613566756