a(n) = floor((1/16)*(16 + 2^n - 8*n + 8*n^2)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =13a(6) =20a(7) =30a(8) =45a(9) =69a(10) =110a(11) =184a(12) =323a(13) =591a(14) =1116a(15) =2154a(16) =4217a(17) =8329a(18) =16538a(19) =32940a(20) =65727a(21) =131283a(22) =262376a(23) =524542a(24) =1048853a(25) =2097453a(26) =4194630a(27) =8388960a(28) =16777595a(29) =33554839