As the title says, it just a doubt about notation. Being more specific it's about the limit of the productory. For example, if we have
$\displaystyle\prod_{i=0}^n (2i+1), \,\, n \in \mathbb{N}$
When $n=0$, do we have $i=0$? Or we just start computing the products when $n>i$?
The notation $$ \prod_{i=j}^n f(i) $$ denotes a product "starting at $j$, and stopping at $n$". So your product, for which $j=n=0$, gives $$ \prod_{i=0}^0 (2i+1) = 2\times0+1=1. $$