Sum{T(i,j)}, 0<=i<=n, 0<=j<=n, T given by A026692.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =33a(5) =75a(6) =167a(7) =361a(8) =791a(9) =1773a(10) =3931a(11) =8539a(12) =18737a(13) =41853a(14) =92693a(15) =201871a(16) =443343a(17) =988491a(18) =2187965a(19) =4772629a(20) =10487105a(21) =23354405a(22) =51673669a(23) =112840057a(24) =248040133a(25) =551900067a(26) =1220786323a(27) =2668013885a(28) =5866328943