a(n) = T(n,0) + T(n,1) + ... + T(n,2n), T given by A027113.

Terms

a(0) =1a(1) =4a(2) =11a(3) =31a(4) =87a(5) =246a(6) =700a(7) =2003a(8) =5758a(9) =16616a(10) =48102a(11) =139625a(12) =406214a(13) =1184138a(14) =3457771a(15) =10112245a(16) =29613029a(17) =86824136a(18) =254840534a(19) =748725393a(20) =2201731878a(21) =6479790418a(22) =19084605389a(23) =56247812793a(24) =165884498711a(25) =489512360356