• General syntax for symbols with a kind of lower and upper limits:

\symbolname_{lowerexpression}^{upperexpression}

• In general, there are two ways how these lower and upper expressions can be placed: centered below and above the symbol or in a subscript / superscript manner. In the first case the symbol name is preceded by the word "big", in the second there is no prefix.
• Note: mimeTeX seems currently only to support the \bigcoprod command.
• Syntax for coproduct symbol:

$$\bigcoprod_{i=k}^{n}$$   gives  

$\bigcoprod_{i=k}^{n}$

• Use font size commands for a nicer picture:

$$\LARGE\bigcoprod_{\small{i=k}}^{\small~n}$$   gives  

$\LARGE\bigcoprod_{\small{i=k}}^{\small~n}$