a(n) = Sum_{k=0..n} T(n,k), T given by A026725.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =18a(5) =40a(6) =80a(7) =176a(8) =352a(9) =769a(10) =1538a(11) =3343a(12) =6686a(13) =14477a(14) =28954a(15) =62505a(16) =125010a(17) =269216a(18) =538432a(19) =1157244a(20) =2314488a(21) =4966260a(22) =9932520a(23) =21282622a(24) =42565244a(25) =91096110a(26) =182192220a(27) =389515284a(28) =779030568a(29) =1664015246