a(n) = (2*n-3)*4^(n-1) - 2*binomial(2*n, n-1).

Terms

a(0) =18a(1) =208a(2) =1372a(3) =7632a(4) =39050a(5) =190112a(6) =895524a(7) =4120528a(8) =18629652a(9) =83088096a(10) =366560568a(11) =1602837280a(12) =6956911962a(13) =30007067456a(14) =128736063316a(15) =549740689872