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 A007655 Standard deviation of A007654. (Formerly M4948) 25
 0, 1, 14, 195, 2716, 37829, 526890, 7338631, 102213944, 1423656585, 19828978246, 276182038859, 3846719565780, 53577891882061, 746243766783074, 10393834843080975, 144767444036350576, 2016350381665827089, 28084137899285228670, 391161580208327374291 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n) corresponds also to one-sixth the area of Fleenor-Heronian triangle with middle side A003500(n). - Lekraj Beedassy, Jul 15 2002 a(n) give all (nontrivial, integer) solutions of Pell equation b(n+1)^2 - 48*a(n+1)^2 = +1 with b(n+1)=A011943(n), n>=0. Number of units of a(n) belongs to a periodic sequence: 0, 1, 4, 5, 6, 9.We conclude that a(n) and a(n+6) have the same number of units. - Mohamed Bouhamida (bhmd95(AT)yahoo.fr), Sep 05 2009 For n>=3, a(n) equals the permanent of the (n-2)X(n-2) tridiagonal matrix with 14's along the main diagonal, and i's along the superdiagonal and the subdiagonal (i is the imaginary unit). - John M. Campbell, Jul 08 2011 For n>1, a(n) equals the number of 01-avoiding words of length n-1 on alphabet {0,1,...,13}. - Milan Janjic, Jan 25 2015 6*a(n)^2 = 6*S(n-1, 14)^2 is the triangular number Tri((T(n, 7) - 1)/2) with Tri = A000217 and T = A053120. This is instance k = 3 of the general k-identity given in a comment to A001109. - Wolfdieter Lang, Feb 01 2016 REFERENCES D. A. Benaron, personal communication. Dino Lorenzini, Z Xiang, Integral points on variable separated curves, Preprint 2016; http://alpha.math.uga.edu/~lorenz/IntegralPoints.pdf N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Indranil Ghosh, Table of n, a(n) for n = 1..874 (terms 1..100 from T. D. Noe) R. Flórez, R. A. Higuita, A. Mukherjee, Alternating Sums in the Hosoya Polynomial Triangle, Article 14.9.5 Journal of Integer Sequences, Vol. 17 (2014). M. Janjic, On Linear Recurrence Equations Arising from Compositions of Positive Integers, 2014; http://matinf.pmfbl.org/wp-content/uploads/2015/01/za-arhiv-18.-1.pdf Tanya Khovanova, Recursive Sequences E. K. Lloyd, The standard deviation of 1, 2, .., n, Pell's equation and rational triangles, The Mathematical Gazette, Vol. 81, No. 491 (Jul., 1997), pp. 231-243. Index entries for linear recurrences with constant coefficients, signature (14,-1). FORMULA a(n) = 14*a(n-1) - a(n-2). G.f.: x^2/(1-14*x+x^2). a(n+1) ~ 1/24*sqrt(3)*(2 + sqrt(3))^(2*n). - Joe Keane (jgk(AT)jgk.org), May 15 2002 a(n+1) = S(n-1, 14), n>=0, with S(n, x) := U(n, x/2) Chebyshev's polynomials of the second kind. S(-1, x) := 0. See A049310. a(n+1) = ((7+4*sqrt(3))^n - (7-4*sqrt(3))^n)/(8*sqrt(3)). a(n+1) = sqrt((A011943(n)^2 - 1)/48), n>=0. Chebyshev's polynomials U(n-2, x) evaluated at x=7. a(n) = A001353(2n)/4. - Lekraj Beedassy, Jul 15 2002 4*a(n+1) + A046184(n) = A055793(n+2) + A098301(n+1) 4*a(n+1) + A098301(n+1) + A055793(n+2) = A046184(n+1) (4*a(n+1))^2 = A098301(2n+1) (conjectures). - Creighton Dement, Nov 02 2004 (4*a(n))^2 = A103974(n)^2 - A011922(n-1)^2. - Paul D. Hanna, Mar 06 2005 a(n) = 13*(a(n-1)+a(n-2))-a(n-3), a(n) = 15*(a(n-1)-a(n-2))+a(n-3). a(n)=14*a(n-1)-a(n-2). - Mohamed Bouhamida (bhmd95(AT)yahoo.fr), May 26 2007 a(n)=b such that (-1)^n/4*Integral_{x=-Pi/2..Pi/2} (sin((2*n-2)*x))/(2-sin(x)) dx = c+b*log(3). - Francesco Daddi, Aug 02 2011 a(n+2) = Sum_{k, 0<=k<=n} A101950(n,k)*13^k. - Philippe Deléham, Feb 10 2012 Product {n >= 1} (1 + 1/a(n)) = 1/3*(3 + 2*sqrt(3)). - Peter Bala, Dec 23 2012 Product {n >= 2} (1 - 1/a(n)) = 1/7*(3 + 2*sqrt(3)). - Peter Bala, Dec 23 2012 a(n) = (A028230(n) - A001570(n))/2. - Richard R. Forberg, Nov 14 2013 EXAMPLE G.f. = x^2 + 14*x^3 + 195*x^4 + 2716*x^5 + 37829*x^6 + 526890*x^7 + ... MAPLE 0, seq(orthopoly[U](n, 7), n=0..30); # Robert Israel, Feb 04 2016 MATHEMATICA lst={}; Do[AppendTo[lst, GegenbauerC[n, 1, 7]], {n, 0, 8^2}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 11 2008 *) LinearRecurrence[{14, -1}, {0, 1}, 20] (* Vincenzo Librandi, Feb 02 2016 *) PROG (Sage) [lucas_number1(n, 14, 1) for n in xrange(0, 20)] # Zerinvary Lajos, Jun 25 2008 (MAGMA) [n le 2 select n-1 else 14*Self(n-1)-Self(n-2): n in [1..70]]; // Vincenzo Librandi, Feb 02 2016 (PARI) concat(0, Vec((x^2/(1-14*x+x^2) + O(x^30)))) \\ Michel Marcus, Feb 02 2016 CROSSREFS Cf. A001353, A003500. Cf. A011945, A067900. Cf. A103974, A011922. Sequence in context: A086946 A158530 A171319 * A208383 A208110 A208842 Adjacent sequences:  A007652 A007653 A007654 * A007656 A007657 A007658 KEYWORD nonn,easy AUTHOR EXTENSIONS Chebyshev comments from Wolfdieter Lang, Nov 08 2002 STATUS approved

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