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 A001080 a(n) = 16*a(n-1) - a(n-2) with a(0) = 0, a(1) = 3. (Formerly M3155 N1278) 9
 0, 3, 48, 765, 12192, 194307, 3096720, 49353213, 786554688, 12535521795, 199781794032, 3183973182717, 50743789129440, 808716652888323, 12888722657083728, 205410845860451325, 3273684811110137472, 52173546131901748227, 831503053299317834160 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also 7*x^2 + 1 is a square; n=7 in PARI script below. - Cino Hilliard, Mar 08 2003 That is, the terms are solutions y of the Pell-Fermat equation x^2 - 7 * y^2 = 1. The corresponding values of x are in A001081. (x,y) = (1,0), (8,3), (127,48), ... - Bernard Schott, Feb 23 2019 The first solution to the equation x^2 - 7*y^2 = 1 is (X(0); Y(0)) = (1; 0) and the other solutions are defined by: (X(n); Y(n))= (8*X(n-1) + 21*Y(n-1); 3*X(n-1) + 8*Y(n-1)), with n >= 1. - Mohamed Bouhamida, Jan 16 2020 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). V. Thébault, Les Récréations Mathématiques. Gauthier-Villars, Paris, 1952, p. 281. LINKS T. D. Noe, Table of n, a(n) for n = 0..200 H. Brocard, Notes élémentaires sur le problème de Peel [sic], Nouvelle Correspondance Mathématique, 4 (1878), 337-343. M. Davis, One equation to rule them all, Trans. New York Acad. Sci. Ser. II, 30 (1968), 766-773. Tanya Khovanova, Recursive Sequences Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992 Index entries for linear recurrences with constant coefficients, signature (16,-1). FORMULA G.f.: 3*x/(1-16*x+x^2). From Mohamed Bouhamida, Sep 20 2006: (Start) a(n) = 15*(a(n-1) + a(n-2)) - a(n-3). a(n) = 17*(a(n-1) - a(n-2)) + a(n-3). (End) a(n) = (sqrt(7)/14)*( (8+3*sqrt(7))^n - (8-3*sqrt(7))^n ), with n >= 0. - Paolo P. Lava, Oct 02 2008 a(n) = 16*a(n-1) - a(n-2) with a(1)=0 and a(2)=3. - Sture Sjöstedt, Nov 18 2011 E.g.f.: exp(8*x)*sinh(3*sqrt(7)*x)/sqrt(7). - G. C. Greubel, Feb 23 2019 MAPLE A001080:=3*z/(1-16*z+z**2); # conjectured (correctly) by Simon Plouffe in his 1992 dissertation MATHEMATICA LinearRecurrence[{16, -1}, {0, 3}, 30] (* Harvey P. Dale, Nov 01 2011 *) CoefficientList[Series[3*x/(1-16*x+x^2), {x, 0, 30}], x] (* G. C. Greubel, Dec 20 2017 *) PROG (PARI) nxsqp1(m, n) = { for(x=1, m, y = n*x*x+1; if(issquare(y), print1(x" ")) ) } (PARI) x='x+O('x^30); concat([0], Vec(3*x/(1-16*x+x^2))) \\ G. C. Greubel, Dec 20 2017 (MAGMA) I:=[0, 3]; [n le 2 select I[n] else 16*Self(n-1) - Self(n-2): n in [1..30]]; (* G. C. Greubel, Dec 20 2017 *) (Sage) (3*x/(1-16*x+x^2)).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, Feb 23 2019 (GAP) a:=[0, 3];; for n in [3..30] do a[n]:=16*a[n-1]-a[n-2]; od; a; # G. C. Greubel, Feb 23 2019 CROSSREFS Equals 3 * A077412. Bisection of A084069. Cf. A048907. Cf. A001081, A010727. - Vincenzo Librandi, Feb 16 2009 Sequence in context: A264730 A024042 A007654 * A099852 A270005 A218382 Adjacent sequences:  A001077 A001078 A001079 * A001081 A001082 A001083 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified December 7 12:17 EST 2021. Contains 349581 sequences. (Running on oeis4.)