a(n) = (2^(n+1) + n^2 + n)/2.

Terms

a(0) =1a(1) =3a(2) =7a(3) =14a(4) =26a(5) =47a(6) =85a(7) =156a(8) =292a(9) =557a(10) =1079a(11) =2114a(12) =4174a(13) =8283a(14) =16489a(15) =32888a(16) =65672a(17) =131225a(18) =262315a(19) =524478a(20) =1048786a(21) =2097383a(22) =4194557a(23) =8388884a(24) =16777516a(25) =33554757a(26) =67109215a(27) =134218106a(28) =268435862a(29) =536871347