Diagonal sums of "correlation triangle" for 2^n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =13a(4) =30a(5) =62a(6) =133a(7) =270a(8) =558a(9) =1125a(10) =2286a(11) =4590a(12) =9253a(13) =18542a(14) =37230a(15) =74533a(16) =149358a(17) =298862a(18) =598309a(19) =1196910a(20) =2394990a(21) =4790565a(22) =9583470a(23) =19168110a(24) =38340901a(25) =76684142a(26) =153377646a(27) =306759973a(28) =613538670a(29) =1227086702