Permutations by total distance
franktaw at netscape.net
franktaw at netscape.net
Thu Dec 7 21:04:32 CET 2006
I was looking at http://www.research.att.com/~njas/sequences/A072949,
which led me to search for and find
http://www.research.att.com/~njas/sequences/A062869. (There should
really be a cross reference.)
A062869 is a table with T(n,k) = the number of permutations of n where
2k = the total distance sum_i abs(i-p(i)). (Equivalently, k = sum_i
max(i-p(i),0).)
A062869 contains two equivalent conjectures; these are obviously
correct.
A072949 also contains a conjecture (in question form). Looking at
A062869, I see a more general conjecture: T(n,k) is even whenever k >=
n. I don't see any start at a proof of this; but maybe somebody else
can. (Or compute some more values and show it's wrong.)
Franklin T. Adams-Watters
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