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 A166468 Number of reduced words of length n in Coxeter group on 4 generators S_i with relations (S_i)^2 = (S_i S_j)^12 = I. 2
 1, 4, 12, 36, 108, 324, 972, 2916, 8748, 26244, 78732, 236196, 708582, 2125728, 6377136, 19131264, 57393360, 172178784, 516532464, 1549585728, 4648722192, 13946061600, 41837869872, 125512664832, 376535160174, 1129596977628 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The initial terms coincide with those of A003946, although the two sequences are eventually different. Computed with MAGMA using commands similar to those used to compute A154638. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, -3). FORMULA G.f. (t^12 + 2*t^11 + 2*t^10 + 2*t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(3*t^12 - 2*t^11 - 2*t^10 - 2*t^9 - 2*t^8 - 2*t^7 - 2*t^6 - 2*t^5 - 2*t^4 - 2*t^3 - 2*t^2 - 2*t + 1). MATHEMATICA CoefficientList[Series[(x^12 + 2 x^11 + 2 x^10 + 2 x^9 + 2 x^8 + 2 x^7 + 2 x^6 + 2 x^5 + 2 x^4 + 2 x^3 + 2 x^2 + 2 x + 1)/(3 x^12 - 2 x^11 - 2 x^10 - 2 x^9 - 2 x^8 - 2 x^7 - 2 x^6 - 2 x^5 - 2 x^4 - 2 x^3 - 2 x^2 - 2 x + 1), {x, 0, 40}], x ] (* Vincenzo Librandi, Apr 29 2014 *) coxG[{12, 3, -2, 30}] (* The coxG program is at A169452 *) (* Harvey P. Dale, May 09 2018 *) CROSSREFS Sequence in context: A165184 A165756 A166328 * A166858 A167105 A167649 Adjacent sequences:  A166465 A166466 A166467 * A166469 A166470 A166471 KEYWORD nonn,easy AUTHOR John Cannon and N. J. A. Sloane, Dec 03 2009 STATUS approved

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Last modified March 25 17:45 EDT 2019. Contains 321477 sequences. (Running on oeis4.)