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i am relatively new here, so if this was asked before, feel free to redirect me. I am searching for an answer in form of a (iterative or recursive) Formula or even better, an algorithm to list them all. But if you know the name of what i am searching for or have some strategy how i could approach this or tips for literature where i can read about it, that would also help.

My question is the following:

How many different boolean functions exist up to permutation of its $n$ variables. That is two functions $f$ and $g$ are considered the same if $$ g(x_1,x_2,\dots,x_n) = f(x_{\sigma^{-1}(1)},x_{\sigma^{-1}(2)},\dots,x_{\sigma^{-1}(n)}) \quad \text{for some} \quad \sigma \in S_n $$ For example, i want to treat $A \wedge \neg B$ as if it was equal to $\neg A \wedge B$, and therefore count it only once.

Edit: I also want to treat $A \wedge \neg B$ as if it was equal to $\neg B \wedge A$. That means, i want to treat functions as equal if they are

  1. semantically equal
  2. semantically different but there exists a permutation of variables that makes them semantically equal
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  • $\begingroup$ Do you want to treat $A\wedge \neg B$ as equal to $\neg A \wedge B$ or as equal to $B\wedge \neg A$? The distinction is important, because the first equality is semantic (unless you consider $\wedge$ as an unordered operator), but the second is "only" syntaxic. $\endgroup$
    – Nathaniel
    May 19, 2022 at 16:04
  • $\begingroup$ To give another example: do you consider $\neg(A\wedge B)$ as equal to $(\neg A)\vee(\neg B)$ or not. $\endgroup$
    – Nathaniel
    May 19, 2022 at 16:07
  • $\begingroup$ I want to treat $A \wedge \neg B$ as equal to $\neg A \wedge B$ and as equal to $B \wedge \neg A$. I want count syntacticly different formulas only once but also, more importantly, i want to count those semanticly different formulas only once that become semantically equal if the variables are permuted in some way. $\endgroup$ May 19, 2022 at 16:09
  • $\begingroup$ To answer your second question: yes i consider them equal. But i want to stress that this is not all i am asking. I want to also consider semantically different functions equal if they become semantically equal if the variables are permuted in some way. So, for example: Traditionally $\neg (A \wedge \neg B) = \neg A \vee B$ but i also want $\neg (A \wedge \neg B) = \neg (B \wedge \neg A)$ which would normally not be equal $\endgroup$ May 19, 2022 at 16:10
  • $\begingroup$ Thank you for the precisions. I suggest you add them to your question. $\endgroup$
    – Nathaniel
    May 19, 2022 at 16:18

1 Answer 1

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You are looking for A003180.

The related sequence A003181 counts functions depending on all variables.

Often one allows further operations: negation of inputs, and negation of the output. The corresponding sequence is then A000370.

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  • $\begingroup$ Thank you a lot. I will read up on that $\endgroup$ May 19, 2022 at 16:32
  • $\begingroup$ Do you also know of an algorithm to list all the functions? $\endgroup$ Dec 22, 2022 at 10:07
  • $\begingroup$ The same approaches used for listing graphs up to isomorphism could also be used here. $\endgroup$ Dec 23, 2022 at 0:25

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