2^(n*(n-1)/2) - n!.A1274292^(n*(n-1)/2) - n!.Terms a(0) =0a(1) =0a(2) =0a(3) =2a(4) =40a(5) =904a(6) =32048a(7) =2092112a(8) =268395136a(9) =68719113856External referencesoeis: A127429