How many non-equivalent formulas that use propositions p1... pn are there? Hi I am stuck on the following question : 
How many non-equivalent formulas that use propositions p1...pn are there?
I'm not quite sure how to find the non-equivalent formulas here, and could someone also explain why the answer is so?
Any help would be really appreciated

Two formulas are equivalent if and only if they have the same truth table. And for any conceivable truth table, there is a formula, say in disjunctive normal form, which has that truth table. 
For each of the $2^n$ possible combinations of truth values of the $p_i$, we have $2$ choices for the truth value of the formula, for a total of $2^{(2^n)}$. 
