a(n) = Sum_{i=0..n, j=0..n} A026648(i,j).

Terms

a(0) =1a(1) =3a(2) =8a(3) =18a(4) =40a(5) =84a(6) =182a(7) =378a(8) =814a(9) =1686a(10) =3626a(11) =7506a(12) =16138a(13) =33402a(14) =71810a(15) =148626a(16) =319522a(17) =661314a(18) =1421714a(19) =2942514a(20) =6325906a(21) =13092690a(22) =28147058a(23) =58255794a(24) =125240050a(25) =259208562a(26) =557254322a(27) =1153345842a(28) =2479497394