a(n) = Sum_{k=0..n} T(n,k), T given by A026758.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =18a(5) =41a(6) =82a(7) =188a(8) =376a(9) =867a(10) =1734a(11) =4020a(12) =8040a(13) =18735a(14) =37470a(15) =87735a(16) =175470a(17) =412715a(18) =825430a(19) =1949624a(20) =3899248a(21) =9245721a(22) =18491442a(23) =44003717a(24) =88007434a(25) =210121733a(26) =420243466a(27) =1006390014a(28) =2012780028a(29) =4833517551