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 A124293 Number of free generators of degree n of symmetric polynomials in 5-noncommuting variables. 5
 1, 1, 2, 6, 22, 91, 406, 1896, 9093, 44279, 217500, 1073657, 5314870, 26352107, 130778039, 649352929, 3225196431, 16021584848, 79597062632, 395469296912, 1964908443531, 9762920818182, 48508934285620, 241027326818991, 1197601448443963, 5950578465799856 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also the number of non-splitable set partitions (see Bergeron et al. reference) of length <=5 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..500 N. Bergeron, C. Reutenauer, M. Rosas and M. Zabrocki, Invariants and Coinvariants of the Symmetric Group in Noncommuting Variables, arXiv:math/0502082 [math.CO], 2005. N. Bergeron, C. Reutenauer, M. Rosas and M. Zabrocki, Invariants and Coinvariants of the Symmetric Group in Noncommuting Variables, Canad. J. Math. 60 (2008), no. 2, 266-296. M. C. Wolf, Symmetric functions of noncommutative elements, Duke Math. J. 2 (1936), 626-637. Index entries for linear recurrences with constant coefficients, signature (10,-32,37,-11). FORMULA O.g.f. (1-9q+24q^2-19q^3)/(1-10q+32q^2-37q^3+11q^4) = (1 - 1/(sum_{k=0}^5 q^k/(prod_{i=1}^k (1-i*q))))/q a(n) = add( A055105(n,k), k=1..5) = add(A055106(n,k),k=1..4) MAPLE a:= n-> (Matrix([[6, 2, 1, 1]]). Matrix(4, (i, j)-> if i=j-1 then 1 elif j=1 then [10, -32, 37, -11][i] else 0 fi)^(n-1))[1, 4]: seq(a(n), n=1..30); # Alois P. Heinz, Sep 05 2008 MATHEMATICA LinearRecurrence[{10, -32, 37, -11}, {1, 1, 2, 6}, 30] (* Jean-François Alcover, Jan 08 2016 *) PROG (MAGMA) I:=[1, 1, 2, 6]; [n le 4 select I[n] else 10*Self(n-1)-32*Self(n-2)+37*Self(n-3)-11*Self(n-4): n in [1..30]]; // Vincenzo Librandi, Jan 09 2016 CROSSREFS Cf. A055105, A055106, A055107, A074664, A001519, A124292, A124294, A124295. Sequence in context: A292318 A150271 A150272 * A107591 A279569 A155866 Adjacent sequences:  A124290 A124291 A124292 * A124294 A124295 A124296 KEYWORD nonn AUTHOR Mike Zabrocki, Oct 24 2006 STATUS approved

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Last modified January 17 14:12 EST 2019. Contains 319225 sequences. (Running on oeis4.)