a(n) = Sum{k=0..n} T(n,k), T given by A026747.

Terms

a(0) =1a(1) =2a(2) =5a(3) =10a(4) =24a(5) =48a(6) =114a(7) =228a(8) =540a(9) =1080a(10) =2558a(11) =5116a(12) =12133a(13) =24266a(14) =57658a(15) =115316a(16) =274600a(17) =549200a(18) =1310817a(19) =2621634a(20) =6271788a(21) =12543576a(22) =30076629a(23) =60153258a(24) =144550655a(25) =289101310a(26) =696176322a(27) =1392352644a(28) =3359516328