a(0) = 1; a(n) = 3*2^n - 1, for n > 0.

Terms

a(0) =1a(1) =5a(2) =11a(3) =23a(4) =47a(5) =95a(6) =191a(7) =383a(8) =767a(9) =1535a(10) =3071a(11) =6143a(12) =12287a(13) =24575a(14) =49151a(15) =98303a(16) =196607a(17) =393215a(18) =786431a(19) =1572863a(20) =3145727a(21) =6291455a(22) =12582911a(23) =25165823a(24) =50331647a(25) =100663295a(26) =201326591a(27) =402653183a(28) =805306367a(29) =1610612735