a(n) is the 2-adic valuation of 1 + 3*{the n-th iterate of 27 with A371094}.

Terms

a(0) =1a(1) =4a(2) =9a(3) =19a(4) =39a(5) =79a(6) =160a(7) =322a(8) =645a(9) =1292a(10) =2585a(11) =5171a(12) =10344a(13) =20689a(14) =41379a(15) =82759a(16) =165520a(17) =331043a(18) =662087a(19) =1324175a(20) =2648352a(21) =5296705a(22) =10593412a(23) =21186825a(24) =42373651a(25) =84747303a(26) =169494607a(27) =338989215a(28) =677978433a(29) =1355956867