a(n) = Sum_{i=0..n} Sum_{j=0..n} A026637(i,j).

Terms

a(0) =1a(1) =3a(2) =7a(3) =17a(4) =37a(5) =79a(6) =163a(7) =333a(8) =673a(9) =1355a(10) =2719a(11) =5449a(12) =10909a(13) =21831a(14) =43675a(15) =87365a(16) =174745a(17) =349507a(18) =699031a(19) =1398081a(20) =2796181a(21) =5592383a(22) =11184787a(23) =22369597a(24) =44739217a(25) =89478459a(26) =178956943a(27) =357913913a(28) =715827853a(29) =1431655735