Dirichlet g.f.: Product_{k>=2} (1 + k^(-s))^(2^(k-1)).

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =16a(5) =40a(6) =64a(7) =144a(8) =262a(9) =544a(10) =1024a(11) =2148a(12) =4096a(13) =8320a(14) =16448a(15) =33060a(16) =65536a(17) =131724a(18) =262144a(19) =525456a(20) =1048832a(21) =2099200a(22) =4194304a(23) =8393568a(24) =16777336a(25) =33562624a(26) =67109892a(27) =134234688a(28) =268435456a(29) =536906368