x^(3n+1)y^(n-1)+2x^(2n+1)y^(2n-1)+x^(n+1)y^(3n-1)
=x^(n+1)y^(n-1)(x^2n+2x^ny^n+y^2n)
=x^(n+1)y^(n-1)(x^n+y^n)^2