a(n) = T(n,0) + T(n,1) + ... + T(n,[ n/2 ]), T given by A026681.

Terms

a(0) =1a(1) =1a(2) =4a(3) =6a(4) =18a(5) =27a(6) =82a(7) =138a(8) =390a(9) =644a(10) =1837a(11) =3242a(12) =8835a(13) =15271a(14) =42086a(15) =76403a(16) =203377a(17) =361636a(18) =974089a(19) =1802727a(20) =4718991a(21) =8559441a(22) =22673687a(23) =42562209a(24) =110006420a(25) =202537249a(26) =529643894a(27) =1005279834a(28) =2572145945a(29) =4791823354