The denominator isn't consecutive

Algebra Level 5

\[\large \dfrac{3}{1\times 2 \times 4} + \dfrac{4}{2 \times 3 \times 5} + \dfrac{5}{3 \times 4 \times 6} + \ldots \]

If the above summation can be expressed as \(\dfrac{a}{b} \) where \(a,b\) are co-prime natural numbers, find \(a+b\).