a(n) = 4^n * n!.A047053a(n) = 4^n * n!.Terms a(0) =1a(1) =4a(2) =32a(3) =384a(4) =6144a(5) =122880a(6) =2949120a(7) =82575360a(8) =2642411520a(9) =95126814720External referencesoeis: A047053