a(n) = 2^(n*(n-1)/2)*n!.A011266a(n) = 2^(n*(n-1)/2)*n!.Terms a(0) =1a(1) =1a(2) =4a(3) =48a(4) =1536a(5) =122880a(6) =23592960a(7) =10569646080External referencesoeis: A011266