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 A172123 Number of ways to place 2 nonattacking bishops on an n X n board. 17
 0, 4, 26, 92, 240, 520, 994, 1736, 2832, 4380, 6490, 9284, 12896, 17472, 23170, 30160, 38624, 48756, 60762, 74860, 91280, 110264, 132066, 156952, 185200, 217100, 252954, 293076, 337792, 387440, 442370, 502944, 569536, 642532 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES E. Bonsdorff, K. Fabel, O. Riihimaa, Schach und Zahl, 1966, p. 51-63 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Christopher R. H. Hanusa, T Zaslavsky, S Chaiken, A q-Queens Problem. IV. Queens, Bishops, Nightriders (and Rooks), arXiv preprint arXiv:1609.00853, a12016 Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = n*(n - 1)*(3*n^2 - n + 2)/6. G.f.: -2*x^2*(x+1)*(x+2)/(x-1)^5. - Vaclav Kotesovec, Mar 25 2010 a(n) = 5*a(n-1)-10*a(n-2)+10*a(n-3)-5*a(n-4)+a(n-5). - Vincenzo Librandi, Apr 29 2013 MATHEMATICA CoefficientList[Series[-2 x (x+1)(x+2)/(x-1)^5, {x, 0, 80}], x] (* Vincenzo Librandi, Apr 29 2013 *) PROG (MAGMA) [n*(n-1)*(3*n^2-n+2)/6: n in [1..40]]; /* or */  I:=[0, 4, 26, 92, 240]; [n le 5 select I[n] else 5*Self(n-1)-10*Self(n-2)+10*Self(n-3)-5*Self(n-4)+Self(n-5): n in [1..40]]; // Vincenzo Librandi, Apr 29 2013 (PARI) a(n)=n*(n-1)*(3*n^2-n+2)/6 \\ Charles R Greathouse IV, Jun 16 2015 CROSSREFS Cf. A036464. Sequence in context: A247194 A102198 A100207 * A298190 A299084 A245457 Adjacent sequences:  A172120 A172121 A172122 * A172124 A172125 A172126 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Jan 26 2010 STATUS approved

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Last modified October 21 23:01 EDT 2020. Contains 337937 sequences. (Running on oeis4.)