For those who love Sequences

Find the sum of the following series :-

$1+\frac { 1 }{ 4 } +\frac { 1\times 3 }{ 4\times 8 } +\frac { 1\times 3\times 5 }{ 4\times 8\times 12 } +..........\infty$

=>The answer can be expressed in the form of $\sqrt { a }$ .

=> Find a.