a(n) = (9*2^n - 6*n - 10)/2.

Terms

a(0) =1a(1) =7a(2) =22a(3) =55a(4) =124a(5) =265a(6) =550a(7) =1123a(8) =2272a(9) =4573a(10) =9178a(11) =18391a(12) =36820a(13) =73681a(14) =147406a(15) =294859a(16) =589768a(17) =1179589a(18) =2359234a(19) =4718527a(20) =9437116a(21) =18874297a(22) =37748662a(23) =75497395a(24) =150994864a(25) =301989805a(26) =603979690a(27) =1207959463a(28) =2415919012a(29) =4831838113