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 A011944 a(n) = 14*a(n-1)-a(n-2) with a(0) = 0, a(1) = 2. 3
 0, 2, 28, 390, 5432, 75658, 1053780, 14677262, 204427888, 2847313170, 39657956492, 552364077718, 7693439131560, 107155783764122, 1492487533566148, 20787669686161950, 289534888072701152 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Standard deviation of A011943. Product x*y, where the pair (x, y) solves for x^2 - 3y^2=1, i.e., a(n)=A001075(n)*A001353(n). - Lekraj Beedassy, Jul 13 2006 LINKS Tanya Khovanova, Recursive Sequences E. Keith Lloyd, The Standard Deviation of 1, 2,..., n: Pell's Equation and Rational Triangles, Math. Gaz. vol 81 (1997), 231-243. Index entries for linear recurrences with constant coefficients, signature (14,-1). FORMULA For all members x of the sequence, 12*x^2 +1 is a square. Lim. n-> Inf. a(n)/a(n-1) = 7 + Sqrt(12). - Gregory V. Richardson, Oct 13 2002 a(n) = [(7+2*Sqrt(12))^(n-1) - (7-2*Sqrt(12))^(n-1)] / (2*Sqrt(12)) - Gregory V. Richardson, Oct 13 2002 a(n) = 13*(a(n-1)+a(n-2))-a(n-3). a(n) = 15*(a(n-1)-a(n-2))+a(n-3). - Mohamed Bouhamida (bhmd95(AT)yahoo.fr), Sep 20 2006 a(n) = Sinh[2n*ArcSinh[Sqrt[3]]]/Sqrt[12] - Herbert Kociemba, Apr 24 2008 G.f.: 2x/(1-14*x+x^2). [From Philippe Deléham, Nov 17 2008] CROSSREFS a(n) = 2 * A007655 = {A001353(2n)}/2. Cf. A011943. Sequence in context: A152280 A061629 A230130 * A271565 A241365 A240771 Adjacent sequences:  A011941 A011942 A011943 * A011945 A011946 A011947 KEYWORD nonn,easy AUTHOR E. K. Lloyd STATUS approved

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Last modified November 15 01:01 EST 2018. Contains 317224 sequences. (Running on oeis4.)