a(n) = n!^2 + (-1)^n.A089043a(n) = n!^2 + (-1)^n.Terms a(0) =0a(1) =5a(2) =35a(3) =577a(4) =14399a(5) =518401a(6) =25401599a(7) =1625702401a(8) =131681894399External referencesoeis: A089043