# 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

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Define "formula". –  Gerry Myerson Oct 2 '12 at 5:56

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 $2^{(2^n)}$.