a(n) = T(3,n), array T given by A047858.

Terms

a(0) =1a(1) =5a(2) =14a(3) =34a(4) =78a(5) =174a(6) =382a(7) =830a(8) =1790a(9) =3838a(10) =8190a(11) =17406a(12) =36862a(13) =77822a(14) =163838a(15) =344062a(16) =720894a(17) =1507326a(18) =3145726a(19) =6553598a(20) =13631486a(21) =28311550a(22) =58720254a(23) =121634814a(24) =251658238a(25) =520093694a(26) =1073741822a(27) =2214592510a(28) =4563402750a(29) =9395240958