How do I integrate $\displaystyle \int{x\sqrt{4x^2+1}}$

I've tried parts with $\displaystyle x=dv$ and $\displaystyle \sqrt{4x^2+1}=u$ and vice-versa and I still don't get the answer. Help please.

N.B. When hinting at the answer, note that I cannot use hyperbolic trig functions, it's off the syllabus.