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 A162921 Number of reduced words of length n in Coxeter group on 4 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I. 0
 1, 4, 12, 36, 102, 288, 816, 2304, 6510, 18396, 51972, 146844, 414894, 1172232, 3312024, 9357768, 26439366, 74701620, 211061436, 596331540, 1684871094, 4760423280, 13450067520, 38001729168, 107369826654, 303361976844 (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 Index entries for linear recurrences with constant coefficients, signature (2, 2, 2, -3). FORMULA G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(3*t^4 - 2*t^3 - 2*t^2 - 2*t + 1) CROSSREFS Sequence in context: A001411 A095350 A084776 * A237045 A291732 A291264 Adjacent sequences:  A162918 A162919 A162920 * A162922 A162923 A162924 KEYWORD nonn AUTHOR John Cannon and N. J. A. Sloane, Dec 03 2009 STATUS approved

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Last modified December 14 09:18 EST 2019. Contains 329979 sequences. (Running on oeis4.)