Sum{T(i,j)}, 0<=i<=n, 0<=j<=n, T given by A026670.

Terms

a(0) =1a(1) =3a(2) =8a(3) =18a(4) =41a(5) =87a(6) =190a(7) =396a(8) =851a(9) =1761a(10) =3754a(11) =7740a(12) =16419a(13) =33777a(14) =71410a(15) =146676a(16) =309319a(17) =634605a(18) =1335680a(19) =2737830a(20) =5753393a(21) =11784519a(22) =24732602a(23) =50628768a(24) =106142095a(25) =217168749a(26) =454874296a(27) =930285390a(28) =1947021505