a(0)=0; thereafter a(n) = (3*n+1)*2^(n-2)+1.

Terms

a(0) =0a(1) =1a(2) =3a(3) =8a(4) =21a(5) =53a(6) =129a(7) =305a(8) =705a(9) =1601a(10) =3585a(11) =7937a(12) =17409a(13) =37889a(14) =81921a(15) =176129a(16) =376833a(17) =802817a(18) =1703937a(19) =3604481a(20) =7602177a(21) =15990785a(22) =33554433a(23) =70254593a(24) =146800641a(25) =306184193a(26) =637534209a(27) =1325400065a(28) =2751463425a(29) =5704253441