a(n) = 2*a(n-1) + 2^(n+1) - 1, a(0) = 0.

Terms

a(0) =0a(1) =3a(2) =13a(3) =41a(4) =113a(5) =289a(6) =705a(7) =1665a(8) =3841a(9) =8705a(10) =19457a(11) =43009a(12) =94209a(13) =204801a(14) =442369a(15) =950273a(16) =2031617a(17) =4325377a(18) =9175041a(19) =19398657a(20) =40894465a(21) =85983233a(22) =180355073a(23) =377487361a(24) =788529153a(25) =1644167169a(26) =3422552065a(27) =7113539585a(28) =14763950081a(29) =30601641985