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Input: The number of elements $m$ and an (positive) integer distance $d$.
Ouput: The number of permutations of $m$ elements which have Kendall-Tau distance $d$ from a fixed permutation.

I think there should be a closed formula. Does anybody know a good reference?

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  • $\begingroup$ The Kendall-Tau distance is also known as the bubble-sort distance. Does this SO question answer your question? $\endgroup$ – Juho Mar 13 '12 at 11:43
  • $\begingroup$ It does! Although not as easy as I hoped, it provides a nice polynomial-time algorithm which should be sufficient for my application. Thanks a lot. $\endgroup$ – RBredereck Mar 13 '12 at 13:51
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    $\begingroup$ Does this sequence in OEIS help? $\endgroup$ – Anthony Labarre Mar 13 '12 at 13:51
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    $\begingroup$ @mrm comment-> answer ? $\endgroup$ – Suresh Venkat Mar 13 '12 at 17:37
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This StackOverflow question answers your question. You might also be interested in this OEIS sequence.

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