Partial sums of A006127, starting at n=1.

Terms

a(0) =3a(1) =9a(2) =20a(3) =40a(4) =77a(5) =147a(6) =282a(7) =546a(8) =1067a(9) =2101a(10) =4160a(11) =8268a(12) =16473a(13) =32871a(14) =65654a(15) =131206a(16) =262295a(17) =524457a(18) =1048764a(19) =2097360a(20) =4194533a(21) =8388859a(22) =16777490a(23) =33554730a(24) =67109187a(25) =134218077a(26) =268435832a(27) =536871316a(28) =1073742257a(29) =2147484111