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 A001973 Expansion of (1+x^3)/((1-x)*(1-x^2)^2*(1-x^3)). (Formerly M2441 N0969) 6
 1, 1, 3, 5, 8, 12, 18, 24, 33, 43, 55, 69, 86, 104, 126, 150, 177, 207, 241, 277, 318, 362, 410, 462, 519, 579, 645, 715, 790, 870, 956, 1046, 1143, 1245, 1353, 1467, 1588, 1714, 1848, 1988 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Contribution from Paul Weisenhorn, Jun 01 2009: (Start) a(1..3)=0; a(n) is the number of partitions of 2*(n+1) with 4 different numbers from the set {1,...,n}; the number of partitions of 2*n + 2 - C and 2*n + 2 + C are equal; example: n=6; 2*n + 2 = 14; a(6)=3; (10,1), (11,1), (12,2), (13,2), (14,3), (15,2), (16,2), (17,1), (18,1). (End) REFERENCES A. Cayley, Numerical tables supplementary to second memoir on quantics, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 2, pp. 276-281. M. Jeger, Einfuehrung in die Kombinatorik, Klett, 1975, pages 110ff. [From Paul Weisenhorn, Jun 01 2009] N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 A. Cayley, Numerical tables supplementary to second memoir on quantics, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 2, pp. 276-281. [Annotated scanned copy] Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992. Index entries for linear recurrences with constant coefficients, signature (2,0,-1,-1,0,2,-1) FORMULA a(n) is the coefficient of x^(2*n+2) in the g.f. Product_{s=1..4} (x^s - x^(n+1))/(1-x^s). - Paul Weisenhorn, Jun 01 2009 a(n) = 2*a(n-1) - a(n-3) - a(n-4) + 2*a(n-6) - a(n-7). Vincenzo Librandi, Jun 11 2012 MAPLE A001973:=(1-z+z**2)/(z+1)/(z**2+z+1)/(z-1)**4; # Simon Plouffe in his 1992 dissertation with(combstruct):ZL:=[st, {st=Prod(left, right), left=Set(U, card=r+1), right=Set(U, card=2)}, unlabeled]: subs(r=2, stack): seq(count(subs(r=2, ZL), size=m), m=6..45) ; # Zerinvary Lajos, Feb 07 2008 MATHEMATICA CoefficientList[Series[(1+x^3)/((1-x)*(1-x^2)^2*(1-x^3)), {x, 0, 40}], x] (* Vincenzo Librandi, Jun 11 2012 *) PROG (PARI) Vec((1+x^3)/((1-x)*(1-x^2)^2*(1-x^3))+O(x^99)) \\ Charles R Greathouse IV, Sep 23 2012 CROSSREFS Sequence in context: A265063 A098202 A164653 * A248374 A020745 A232896 Adjacent sequences:  A001970 A001971 A001972 * A001974 A001975 A001976 KEYWORD nonn,easy AUTHOR STATUS approved

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