a(n) = A255300(2^k-1).

Terms

a(0) =1a(1) =4a(2) =16a(3) =56a(4) =196a(5) =680a(6) =2348a(7) =8096a(8) =27892a(9) =96056a(10) =330748a(11) =1138768a(12) =3920644a(13) =13498088a(14) =46471180a(15) =159990272a(16) =550811156a(17) =1896319640a(18) =6528602140a(19) =22476505520a(20) =77381536036a(21) =266407155784a(22) =917179667500