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 A060422 Number of acute triangles made from vertices of a regular n-gon. 1
 0, 0, 0, 1, 0, 5, 2, 14, 8, 30, 20, 55, 40, 91, 70, 140, 112, 204, 168, 285, 240, 385, 330, 506, 440, 650, 572, 819, 728, 1015, 910, 1240, 1120, 1496, 1360, 1785, 1632, 2109, 1938, 2470, 2280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (1,3,-3,-3,3,1,-1). FORMULA a(n) = n*(n+1)*(n-1)/24 when n is odd, otherwise n*(n-2)*(n-4)/24. G.f.: x^3*(2*x^2-x+1) / ((x-1)^4*(x+1)^3). - Colin Barker, Dec 24 2012 a(n) = n*(2*n^2-6*n+7-3*(2*n-3)*(-1)^n)/48. - Luce ETIENNE, Mar 19 2015 MATHEMATICA LinearRecurrence[{1, 3, -3, -3, 3, 1, -1}, {0, 0, 0, 1, 0, 5, 2}, 50] (* Vincenzo Librandi, Dec 25 2012 *) CROSSREFS Union of A000330, A007290. Sequence in context: A158868 A104634 A194008 * A213751 A185781 A265434 Adjacent sequences:  A060419 A060420 A060421 * A060423 A060424 A060425 KEYWORD easy,nonn AUTHOR Sen-Peng Eu, Apr 05 2001 STATUS approved

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Last modified July 15 14:28 EDT 2019. Contains 325031 sequences. (Running on oeis4.)