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 A056771 a(n) = a(-n) = 34*a(n-1) - a(n-2), and a(0)=1, a(1)=17. 13
 1, 17, 577, 19601, 665857, 22619537, 768398401, 26102926097, 886731088897, 30122754096401, 1023286908188737, 34761632124320657, 1180872205318713601, 40114893348711941777, 1362725501650887306817, 46292552162781456490001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The sequence satisfies the Pell equation a(n)^2 - 18 * A202299(n+1)^2 = 1. - Vincenzo Librandi, Dec 19 2011 Also numbers n such that n - 1 and 2*n + 2 are squares. - Arkadiusz Wesolowski, Mar 15 2015 And they, n - 1 and 2*n + 2, are the squares of A005319 and A003499. - Michel Marcus, Mar 15 2015 This sequence {a(n)} gives all the nonnegative integer solutions of the Pell equation a(n)^2 - 32*(3*A091761(n))^2 = +1. - Wolfdieter Lang, Mar 09 2019 LINKS Seiichi Manyama, Table of n, a(n) for n = 0..600 (terms 0..200 from Vincenzo Librandi) Tanya Khovanova, Recursive Sequences Index entries for sequences related to Chebyshev polynomials. Index entries for linear recurrences with constant coefficients, signature (34,-1). FORMULA a(n) = (r^n + 1/r^n)/2 with r = 17 + sqrt(17^2-1). a(n) = 16*A001110(n) + 1 = A001541(2n) = (4*A001109(n))^2 + 1 = 3*A001109(2n-1) - A001109(2n-2) = A001109(2n) - 3*A001109(2n-1). a(n) = T(n, 17) = T(2*n, 3) with T(n, x) Chebyshev's polynomials of the first kind. See A053120. T(n, 3)= A001541(n). G.f.: (1-17*x)/(1-34*x+x^2). G.f.: (1 - 17*x / (1 - 288*x / (17 - x))). - Michael Somos, Apr 05 2019 a(n) = cosh(2n*arcsinh(sqrt(8))). - Herbert Kociemba, Apr 24 2008 a(n) = (a^n + b^n)/2 where a = 17 + 12*sqrt(2) and b = 17 - 12*sqrt(2); sqrt(a(n)-1)/4 = A001109(n). - James R. Buddenhagen, Dec 09 2011 a(-n) = a(n). - Michael Somos, May 28 2014 a(n) = sqrt(1 + 32*9*A091761(n)^2), n >= 0. See one of the Pell comments above. - Wolfdieter Lang, Mar 09 2019 EXAMPLE G.f. = 1 + 17*x + 577*x^2 + 19601*x^3 + 665857*x^4 + 22619537*x^5 + ... MATHEMATICA LinearRecurrence[{34, -1}, {1, 17}, 30] (* Vincenzo Librandi, Dec 18 2011 *) a[ n_] := ChebyshevT[ 2 n, 3]; (* Michael Somos, May 28 2014 *) PROG (Sage) [lucas_number2(n, 34, 1)/2 for n in range(0, 15)] # Zerinvary Lajos, Jun 27 2008 (Magma) I:=[1, 17]; [n le 2 select I[n] else 34*Self(n-1)-Self(n-2): n in [1..20]]; // Vincenzo Librandi, Dec 18 2011 (Maxima) makelist(expand(((17+sqrt(288))^n+(17-sqrt(288))^n))/2, n, 0, 15); // Vincenzo Librandi, Dec 18 2011 (PARI) {a(n) = polchebyshev( n, 1, 17)}; /* Michael Somos, Apr 05 2019 */ CROSSREFS Cf. A001075, A001541, A001091, A001079, A023038, A011943, A001081, A023039, A001085 and note relationship with square triangular number sequences A001110 and A001109. A091761. Row 3 of array A188644. Sequence in context: A012069 A191865 A249862 * A041547 A041544 A202407 Adjacent sequences: A056768 A056769 A056770 * A056772 A056773 A056774 KEYWORD nonn,easy AUTHOR Henry Bottomley, Aug 16 2000 EXTENSIONS More terms from James A. Sellers, Sep 07 2000 Chebyshev comments from Wolfdieter Lang, Nov 29 2002 STATUS approved

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