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A129441
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G.f. x*(1-x^2-x^3)/ ((1+x+x^2) * (x^4-x^3-x^2-2*x+1) ).
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1, 1, 2, 7, 16, 39, 100, 248, 618, 1546, 3858, 9631, 24049, 60041, 149903, 374266, 934427, 2332981, 5824753, 14542648, 36308602, 90651625, 226329747, 565077072, 1410826915, 3522409024, 8794392287, 21956943442, 54819861280, 136868649264
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| The case q=1 on page 132 of the Billey et al. paper.
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LINKS
| Sara Billey, Gregory Warrington, Kazhdan-Lusztig Polynomials for 321-hexagon-avoiding permutations, J. Algebr. Combinat. 13 (2) (2001) 111-136.
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FORMULA
| a(n) = a(n-1) +2*a(n-2) +4*a(n-3) +a(n-4) -a(n-6).
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MATHEMATICA
| p[x_, q_] = (-1 + q^2*x^2 + q^3*x^3)/((1 + q*x + q^2*x^2)*(-1 + x + q*x + q^2*x^2 + q^2*x^3 - q^4*x^4)); Table[ SeriesCoefficient[Series[p[x, 1], {x, 0, 30}], n], {n, 0, 30}]
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CROSSREFS
| Sequence in context: A176805 A042243 A041887 * A093971 A065497 A131727
Adjacent sequences: A129438 A129439 A129440 * A129442 A129443 A129444
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KEYWORD
| nonn
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AUTHOR
| Roger L. Bagula (rlbagulatftn(AT)yahoo.com), Jun 08 2007
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EXTENSIONS
| Definition simplified - the Assoc. Eds of the OEIS, Mar 28 2010
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