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

Terms

a(0) =2a(1) =6a(2) =13a(3) =24a(4) =41a(5) =68a(6) =113a(7) =192a(8) =337a(9) =612a(10) =1145a(11) =2192a(12) =4265a(13) =8388a(14) =16609a(15) =33024a(16) =65825a(17) =131396a(18) =262505a(19) =524688a(20) =1049017a(21) =2097636a(22) =4194833a(23) =8389184a(24) =16777841a(25) =33555108a(26) =67109593a(27) =134218512a(28) =268436297a(29) =536871812