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 A033586 a(n) = 4*n*(2*n + 1). 22
 0, 12, 40, 84, 144, 220, 312, 420, 544, 684, 840, 1012, 1200, 1404, 1624, 1860, 2112, 2380, 2664, 2964, 3280, 3612, 3960, 4324, 4704, 5100, 5512, 5940, 6384, 6844, 7320, 7812, 8320, 8844, 9384, 9940, 10512, 11100, 11704, 12324, 12960, 13612, 14280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of possible king moves on an (n+1) X (n+1) chessboard. - Ulrich Schimke (ulrschimke(AT)aol.com) Sequence found by reading the line from 0, in the direction 0, 12, ..., in the square spiral whose vertices are the triangular numbers A000217. Opposite numbers to the members of A085250 in the same spiral. - Omar E. Pol, Sep 03 2011 Sum of the numbers from 3n to 5n. - Wesley Ivan Hurt, Dec 22 2015 a(n) is the second Zagreb index of the friendship graph F[n]. The second Zagreb index of a simple connected graph is the sum of the degree products d(i)d(j) over all edges ij of the graph. The friendship graph (or Dutch windmill graph) F[n] can be constructed by joining n copies of the cycle graph C with a common vertex. - Emeric Deutsch, Nov 09 2016 REFERENCES E. Bonsdorff, K. Fabel and O. Riihimaa, Schach und Zahl (Chess and numbers), Walter Rau Verlag, Dusseldorf, 1966. LINKS G. C. Greubel, Table of n, a(n) for n = 0..5000 Tim Krabbe, Open Chess Diary, see item 221 Wikipedia, Friendship graph Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA Binomial transform of [12, 28, 16, 0, 0, 0, ...] = (12, 40, 84, 144, 220, ...). - Gary W. Adamson, Oct 24 2007 a(n) = 4 * A014105(n). - Johannes W. Meijer, Feb 04 2010 a(n) = 16*n+a(n-1)-4 (with a(0)=0). - Vincenzo Librandi, Aug 05 2010 a(0)=0, a(1)=12, a(2)=40, a(n) = 3*a(n-1)-3*a(n-2)+a(n-3) for n>2. - Harvey P. Dale, May 10 2011 G.f.: 4*x*(3+x)/(1-3*x+3*x^2-x^3). - Colin Barker, Jan 06 2012 From Wesley Ivan Hurt, Feb 25 2014, Dec 22 2015: (Start) a(n) = A008586(n) * A005408(n). a(n) = Sum_{i=3n..5n} i. a(-n) = A085250(n). (End) E.g.f.: (8*x^2 + 12*x)*exp(x). - G. C. Greubel, Jul 16 2017 EXAMPLE 3 X 3 board: king has 4*5 moves, 4*3 moves and 1*8 moves, so a(2)=40. a(2)=40. Indeed, the friendship graph F has 2 edges with end-point degrees 2,2 and 4 edges with end-point degrees 2,4. Then the second Zagreb index is 2*4 + 4*8 = 40. - Emeric Deutsch, Nov 09 2016 MAPLE A033586:=n->4*n*(2*n+1); seq(A033586(n), n=0..60); # Wesley Ivan Hurt, Feb 25 2014 MATHEMATICA Table[4n*(2n + 1), {n, 0, 60}] (* Stefan Steinerberger, Apr 08 2006 *) LinearRecurrence[{3, -3, 1}, {0, 12, 40}, 60] (* Harvey P. Dale, May 19 2011 *) PROG (PARI) a(n)=4*n*(2*n+1) \\ Charles R Greathouse IV, Jul 16, 2011 (MAGMA) [4*n*(2*n + 1) : n in [0..50]]; // Wesley Ivan Hurt, Dec 22 2015 CROSSREFS Cf. A035005 (Queen), A035006 (Rook), A035008 (Knight), A002492 (Bishop) and A049450 (Pawn). Cf. A000217, A005408, A008586, A014105, A085250. Sequence in context: A114815 A175583 A109766 * A211786 A320252 A180093 Adjacent sequences:  A033583 A033584 A033585 * A033587 A033588 A033589 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from Erich Friedman Crossref added, minor errors corrected and edited by Johannes W. Meijer, Feb 04 2010 STATUS approved

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Last modified August 17 22:59 EDT 2019. Contains 326059 sequences. (Running on oeis4.)