$$\frac{ 1 }{ 3 \times 7 } \frac{ 1 }{ 7 \times 11 } \frac{ 1 }{ 11 \times 15 } \frac{ 1 }{ 15 \times 19 }$$
$\frac{1}{76039425}\approx 0.000000013$
$\frac{1}{3 ^ {3} \cdot 5 ^ {2} \cdot 7 ^ {2} \cdot 11 ^ {2} \cdot 19} = 1.315107261792156 \times 10^{-8}$
