G.f.: g.f. for A001411 / g.f. for A004018.

Terms

a(0) =1a(1) =0a(2) =8a(3) =4a(4) =48a(5) =68a(6) =284a(7) =684a(8) =1816a(9) =5608a(10) =12684a(11) =42068a(12) =92916a(13) =304100a(14) =688988a(15) =2170020a(16) =5088784a(17) =15436172a(18) =37281880a(19) =109786204a(20) =271062388a(21) =781016892a(22) =1958863988a(23) =5555714820a(24) =14090644980a(25) =39503105472a(26) =101000072900a(27) =280693435596