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 A070333 Expansion of (1 + x)*(1 - x + x^2)/((1 - x)^4*(1 + x + x^2)). 3
 1, 3, 6, 12, 21, 33, 50, 72, 99, 133, 174, 222, 279, 345, 420, 506, 603, 711, 832, 966, 1113, 1275, 1452, 1644, 1853, 2079, 2322, 2584, 2865, 3165, 3486, 3828, 4191, 4577, 4986, 5418, 5875, 6357, 6864, 7398, 7959, 8547, 9164, 9810, 10485 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) is the number of 3 X 3 matrices with nonnegative integer entries such that every row sum, column sum and the trace of the matrix is n. - Sharon Sela (sharonsela(AT)hotmail.com), May 20 2002 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 Index entries for linear recurrences with constant coefficients, signature (3,-3,2,-3,3,-1). FORMULA a(n) = 1 + 7*n/6 + n^2/2 + n^3/9 + 2*A049347(n-1)/9. - R. J. Mathar, Dec 03 2010 From Mircea Merca, Dec 03 2010: (Start) a(n) = round((2*n + 3)*(n^2 + 3*n + 6)/18). a(n) = floor((n + 2)*(2*n^2 + 5*n + 11)/18). a(n) = ceiling((n + 1)*(2*n^2 + 7*n + 14)/18). a(n) = round((n + 1)*(2*n^2 + 7*n + 14)/18). a(n) = a(n-3) + n^2 + 2 for n > 2. (End) E.g.f.: exp(x)*(1 + x*(32 + x*(15 + 2*x))/18) + 4*exp(-x/2)*sin(sqrt(3)*x/2)/(9*sqrt(3)). - Stefano Spezia, Oct 28 2022 MAPLE A049347 := proc(n) op(1+(n mod 3), [1, -1, 0]) ; end proc: A070333 := proc(n) 1+7*n/6+n^2/2+n^3/9+2*A049347(n-1)/9 ; end proc: # R. J. Mathar, Dec 03 2010 MATHEMATICA CoefficientList[ Series[(1 + x^3)/(1 - 3*x + 3*x^2 - 2*x^3 + 3*x^4 - 3*x^5 + x^6), {x, 0, 45}], x] PROG (Magma) [Round((2*n+3)*(n^2+3*n+6)/18): n in [0..50]]; // Vincenzo Librandi, Jun 25 2011 (PARI) Vec((1+x)*(1-x+x^2)/((1-x)^4*(1+x+x^2))+O(x^99)) \\ Charles R Greathouse IV, Sep 27 2012 CROSSREFS Cf. A059827, A001844, A002817. Sequence in context: A246866 A053479 A290768 * A011779 A161809 A084439 Adjacent sequences: A070330 A070331 A070332 * A070334 A070335 A070336 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 11 2002 STATUS approved

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Last modified April 21 12:56 EDT 2024. Contains 371870 sequences. (Running on oeis4.)