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 A161436 Number of reduced words of length n in the Weyl group A_4. 1
 1, 4, 9, 15, 20, 22, 20, 15, 9, 4, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Computed with MAGMA using commands similar to those used to compute A161409. REFERENCES N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche I.) J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under PoincarĂ© polynomial. LINKS FORMULA G.f. for A_m is the polynomial Product_{k=1..m}(1-x^(k+1))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A008302. MATHEMATICA CoefficientList[Series[(1 - x^2) (1 - x^3) (1 - x^4) (1 - x^5) / (1 - x)^4, {x, 0, 20}], x] (* Vincenzo Librandi, Aug 23 2016 *) CROSSREFS Cf. A008302, A161409. Sequence in context: A313221 A313222 A313223 * A274088 A313224 A313225 Adjacent sequences:  A161433 A161434 A161435 * A161437 A161438 A161439 KEYWORD nonn AUTHOR John Cannon and N. J. A. Sloane, Nov 30 2009 STATUS approved

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Last modified August 20 00:52 EDT 2018. Contains 313902 sequences. (Running on oeis4.)