Erroneous version of A263656.

Terms

a(0) =0a(1) =2a(2) =4a(3) =6a(4) =12a(5) =30a(6) =70a(7) =168a(8) =412a(9) =1014a(10) =2514a(11) =6270a(12) =15702a(13) =39468a(14) =99516a(15) =251586a(16) =637500