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is there a difference equation for this, or a closed form for rate of convergence, as a function of initial number chosen? (Key?: last digit of descending-arranged number is always greater then the last digit of the ascending-arranged number while the middle digits are always the same, so you always wind up with 9 in the middle so it's a matter of having the 4 and the 5 converge)radek (talk) 08:36, 24 November 2009 (UTC)