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 A163102 a(n) = n^2*(n+1)^2/2. 15
 0, 2, 18, 72, 200, 450, 882, 1568, 2592, 4050, 6050, 8712, 12168, 16562, 22050, 28800, 36992, 46818, 58482, 72200, 88200, 106722, 128018, 152352, 180000, 211250, 246402, 285768, 329672, 378450, 432450, 492032, 557568, 629442, 708050, 793800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Row sums of triangle A163282. Also, the number of nonattacking placements of 2 rooks on an (n+1) X (n+1) board. - Thomas Zaslavsky, Jun 26 2010 If P_{k}(n) is the n-th k-gonal number, then a(n) = P_{s}(n+1)*P_{t}(n+1) - P_{s+1}(n+1)*P_{t-1}(n+1) for s=t+1. - Bruno Berselli, Sep 05 2014 Subsequence of A000982, see formula. - David James Sycamore, Jul 31 2018 Number of edges in the (n+1) X (n+1) rook complement graph. - Freddy Barrera, May 02 2019 REFERENCES Seth Chaiken, Christopher R. H. Hanusa, and Thomas Zaslavsky, A q-queens problem, in preparation. - Thomas Zaslavsky, Jun 26 2010 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Seth Chaiken, Christopher R. H. Hanusa and Thomas Zaslavsky, A q-Queens Problem. IV. Queens, Bishops, Nightriders (and Rooks), arXiv preprint arXiv:1609.00853 [math.CO], 2016-2020. A. Umar, Combinatorial Results for Semigroups of Orientation-Preserving Partial Transformations, J. Int. Seq., Vol. 14 (2011), Article 11.7.5. Eric Weisstein's World of Mathematics, Rook Complement Graph. Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = 2*A000537(n) = A035287(n+1)/2. - Omar E. Pol, Nov 29 2011 G.f.: 2*x*(1+4*x+x^2) / (1-x)^5. - R. J. Mathar, Nov 30 2011 Let t(n) = A000217(n). Then a(n) = (t(n-1)*(t(n)+t(n+1)) + t(n)*(t(n-1)+t(n+1)) + t(n+1)*(t(n-1)+t(n)))/3. - J. M. Bergot, Jun 21 2012 a(n) = A000982(n*(n+1)). - David James Sycamore, Jul 31 2018 From Amiram Eldar, Nov 02 2021: (Start) Sum_{n>=1} 1/a(n) = 2*Pi^2/3 - 6. Sum_{n>=1} (-1)^(n+1)/a(n) = 6 - 8*log(2). (End) MATHEMATICA CoefficientList[Series[2*x*(1+4*x+x^2)/(1-x)^5, {x, 0, 40}], x] (* Vincenzo Librandi, Mar 26 2012 *) PROG (MAGMA) [n^2*(n+1)^2/2: n in [0..40]]; // Vincenzo Librandi, Mar 26 2012 (PARI) a(n)=n^2*(n+1)^2/2 \\ Charles R Greathouse IV, Oct 07 2015 (GAP) List([0..40], n->(n*(n+1))^2/2); # Muniru A Asiru, Aug 02 2018 CROSSREFS Column k=2 of A144084. Cf. A006002, A099903, A163274, A163275, A163276, A163277, A163282, A000982. Sequence in context: A316902 A316904 A196812 * A073976 A120361 A120358 Adjacent sequences:  A163099 A163100 A163101 * A163103 A163104 A163105 KEYWORD nonn,easy AUTHOR Omar E. Pol, Jul 24 2009 STATUS approved

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Last modified July 5 06:18 EDT 2022. Contains 355088 sequences. (Running on oeis4.)