a(n) = Sum_{i=0..n} Sum_{j=0..n} A026626(i,j).

Terms

a(0) =1a(1) =3a(2) =8a(3) =18a(4) =40a(5) =84a(6) =174a(7) =354a(8) =716a(9) =1440a(10) =2890a(11) =5790a(12) =11592a(13) =23196a(14) =46406a(15) =92826a(16) =185668a(17) =371352a(18) =742722a(19) =1485462a(20) =2970944a(21) =5941908a(22) =11883838a(23) =23767698a(24) =47535420a(25) =95070864a(26) =190141754a(27) =380283534a(28) =760567096a(29) =1521134220