a(n) = 7*2^n - 3*n - 6.

Terms

a(0) =1a(1) =5a(2) =16a(3) =41a(4) =94a(5) =203a(6) =424a(7) =869a(8) =1762a(9) =3551a(10) =7132a(11) =14297a(12) =28630a(13) =57299a(14) =114640a(15) =229325a(16) =458698a(17) =917447a(18) =1834948a(19) =3669953a(20) =7339966a(21) =14679995a(22) =29360056a(23) =58720181a(24) =117440434a(25) =234880943a(26) =469761964a(27) =939524009a(28) =1879048102a(29) =3758096291