Universal quadratic form

A universal quadratic form is a specific type of quadratic form that has the property of representing all possible integers through its integer values. In other words, a quadratic form is called "universal" if it can represent every integer as a value of the form \( ax^2 + bxy + cy^2 \) (for integer coefficients \(a\), \(b\), and \(c\)) for appropriate integer inputs \(x\) and \(y\).