Phi(binomial(2*n,n)*n^3).

Terms

a(0) =0a(1) =1a(2) =16a(3) =144a(4) =1536a(5) =7200a(6) =51840a(7) =282240a(8) =1474560a(9) =7464960a(10) =55296000a(11) =200724480a(12) =1051066368a(13) =6167715840a(14) =21459271680a(15) =114960384000a(16) =523197480960