Indefinite Integration

If \(\int \frac{x^3 \mathrm{~d} x}{\sqrt{1+x^2}}=\mathrm{a}\left(1+x^2\right) \sqrt{1+x^2}+\mathrm{b} \sqrt{1+x^2}+\mathrm{c}\)
(where \(\mathrm{c}\) is a constant of integration), then the value of \(3 \mathrm{ab}\) is