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 A069515 Number of transpositions (interchanges of adjacent digits, sometimes called inversions) needed to change all n-digit base 3 numbers into nondecreasing order. 0
 0, 3, 24, 135, 648, 2835, 11664, 45927, 174960, 649539, 2361960, 8444007, 29760696, 103630995, 357128352, 1219657095, 4132485216, 13904090883, 46490458680, 154580775111, 511395045480, 1684116865683, 5523066491184 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The corresponding problem for base 2 numbers gives a(n)=A001793(n-1) for n=2,3,4,.... LINKS Index entries for linear recurrences with constant coefficients, signature (9,-27,27). FORMULA a(n) = 3a(n-1)+(2n-1)3^(n-2). a(n) = (n-1)(n+1)3^(n-2). - Ralf Stephan, Sep 02 2003 G.f.: 3*x^2*(1-x)/(1-3*x)^3. - Colin Barker, May 01 2012 EXAMPLE The base 3 number 1210 requires 4 transpositions: 1210->1201->1021->0121->0112. CROSSREFS Cf. A064017. Sequence in context: A305543 A183900 A001089 * A206949 A215636 A056350 Adjacent sequences:  A069512 A069513 A069514 * A069516 A069517 A069518 KEYWORD nonn,base,easy AUTHOR John W. Layman, Apr 16 2002 EXTENSIONS Corrected by T. D. Noe, Nov 01 2006 STATUS approved

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Last modified August 12 16:40 EDT 2020. Contains 336439 sequences. (Running on oeis4.)