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

Terms

a(0) =2a(1) =5a(2) =13a(3) =27a(4) =49a(5) =83a(6) =137a(7) =227a(8) =385a(9) =675a(10) =1225a(11) =2291a(12) =4385a(13) =8531a(14) =16777a(15) =33219a(16) =66049a(17) =131651a(18) =262793a(19) =525011a(20) =1049377a(21) =2098035a(22) =4195273a(23) =8389667a(24) =16778369a(25) =33555683a(26) =67110217a(27) =134219187a(28) =268437025a(29) =536872595