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 A004302 a(n) = n^2*(n+1)^2*(n+2)/12. 6
 0, 1, 12, 60, 200, 525, 1176, 2352, 4320, 7425, 12100, 18876, 28392, 41405, 58800, 81600, 110976, 148257, 194940, 252700, 323400, 409101, 512072, 634800, 780000, 950625, 1149876, 1381212, 1648360, 1955325 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Kekulé numbers for certain benzenoids. - Emeric Deutsch, Jun 19 2005 a(n-2), n>=3, is the number of ways to have n identical objects in m=3 of altogether n distinguishable boxes (n-3 boxes stay empty). - Wolfdieter Lang, Nov 13 2007 Starting with offset 1 = row sums of triangle A096948 and binomial transform of {1, 11, 37, 55, 38, 10, 0, 0, 0,...]. - Gary W. Adamson, Aug 08 2008 Product of sum of first n Triangular numbers and Triangular number(n). - Vladimir Joseph Stephan Orlovsky, Oct 13 2009 REFERENCES T. A. Gulliver, Sequences from Cubes of Integers, Int. Math. Journal, 4 (2003), 439-445. S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p.233, # 11). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 P. Aluffi, Degrees of projections of rank loci, arXiv:1408.1702 [math.AG], 2014. ["After compiling the results of many explicit computations, we noticed that many of the numbers d_{n,r,S} appear in the existing literature in contexts far removed from the enumerative geometry of rank conditions; we owe this surprising (to us) observation to perusal of [Slo14]."] Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1). FORMULA From Paul Barry, Feb 03 2005: (Start) G.f.: x*(1 + 6*x + 3*x^2)/(1 - x)^6. a(n) = C(n, 2)*C(n+1, 3). (End) a(n) = 3*C(n,3)^2/n, n>= 2. - Zerinvary Lajos, May 09 2008 a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>5. - Harvey P. Dale, Oct 19 2014 a(n) = A000217(n)*A000292(n). - Bruno Berselli, Jan 13 2015 a(n) = Sum_{k=0..n} Sum_{i=0..n} i*C(k+1,k-1). - Wesley Ivan Hurt, Sep 21 2017 a(n) = Sum_{i=0..n} (n+2)*(n-i)^3/3. - Bruno Berselli, Oct 31 2017 EXAMPLE a(3)=60 because n=5 identical balls can be put into m=3 of n=5 distinguishable boxes in binomial(5,3)*(3!/(2!*1!)+ 3!/(1!*2!) ) = 10*(3+3) = 60 ways. The m=3 part partitions of 5, namely (1^2,3) and (1,2^2) specify the filling of each of the 10 possible three-box choices. - Wolfdieter Lang, Nov 13 2007 MAPLE a:=n->n^2*(n+1)^2*(n+2)/12: seq(a(n), n=0..33); # Emeric Deutsch, Jun 19 2005 MATHEMATICA Table[n^2 (n+1)^2 (n+2)/12, {n, 0, 30}] (* or *) LinearRecurrence[{6, -15, 20, -15, 6, -1}, {0, 1, 12, 60, 200, 525}, 30] (* Harvey P. Dale, Oct 19 2014 *) PROG (MAGMA) [n^2*(n+1)^2*(n+2)/12: n in [0..40]]; // Vincenzo Librandi, May 22 2011 (Haskell) a004302 0 = 0 a004302 n = a103371 (n + 1) 2 -- Reinhard Zumkeller, Apr 04 2014 (PARI) a(n)=n^2*(n+1)^2*(n+2)/12 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Third column of triangle A103371. Cf. A000217, A000292, A096948. Sequence in context: A174642 A061624 A213818 * A277106 A000554 A012289 Adjacent sequences:  A004299 A004300 A004301 * A004303 A004304 A004305 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified January 23 19:12 EST 2020. Contains 331175 sequences. (Running on oeis4.)