a(n) = Sum{T(i,j)}, 0<=j<=i, 0<=i<=n, T given by A026907.

Terms

a(0) =1a(1) =27a(2) =127a(3) =399a(4) =1039a(5) =2439a(6) =5383a(7) =11439a(8) =23743a(9) =48567a(10) =98455a(11) =198495a(12) =398863a(13) =799911a(14) =1602343a(15) =3207567a(16) =6418399a(17) =12840471a(18) =25685047a(19) =51374655a(20) =102754351a(21) =205514247a(22) =411034567a(23) =822075759a(24) =1644158719a(25) =3288325239a(26) =6576658903a(27) =13153326879a(28) =26306663503a(29) =52613337447