a(n) = 36*2^n - 5 (n>=1).

Terms

a(0) =67a(1) =139a(2) =283a(3) =571a(4) =1147a(5) =2299a(6) =4603a(7) =9211a(8) =18427a(9) =36859a(10) =73723a(11) =147451a(12) =294907a(13) =589819a(14) =1179643a(15) =2359291a(16) =4718587a(17) =9437179a(18) =18874363a(19) =37748731a(20) =75497467a(21) =150994939a(22) =301989883a(23) =603979771a(24) =1207959547a(25) =2415919099a(26) =4831838203a(27) =9663676411a(28) =19327352827a(29) =38654705659