a(n) = 2^n + n.

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =20a(5) =37a(6) =70a(7) =135a(8) =264a(9) =521a(10) =1034a(11) =2059a(12) =4108a(13) =8205a(14) =16398a(15) =32783a(16) =65552a(17) =131089a(18) =262162a(19) =524307a(20) =1048596a(21) =2097173a(22) =4194326a(23) =8388631a(24) =16777240a(25) =33554457a(26) =67108890a(27) =134217755a(28) =268435484a(29) =536870941