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 A098244 First differences of Chebyshev polynomials S(n,171)=A097844(n) with Diophantine property. 5
 1, 170, 29069, 4970629, 849948490, 145336221161, 24851643870041, 4249485765555850, 726637214266180309, 124250714153751276989, 21246145483077202184810, 3632966626892047822325521, 621216047053057100415479281, 106224311079445872123224631530 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS (13*b(n))^2 - 173*a(n)^2 = -4 with b(n)=A097845(n) give all positive solutions of this Pell equation. LINKS Indranil Ghosh, Table of n, a(n) for n = 0..446 Tanya Khovanova, Recursive Sequences Giovanni Lucca, Integer Sequences and Circle Chains Inside a Hyperbola, Forum Geometricorum (2019) Vol. 19, 11-16. Index entries for linear recurrences with constant coefficients, signature (171, -1). FORMULA a(n) = ((-1)^n)*S(2*n, 13*I) with the imaginary unit I and the S(n, x)=U(n, x/2) Chebyshev polynomials. G.f.: (1-x)/(1-171*x+x^2). a(n) = S(n, 171) - S(n-1, 171) = T(2*n+1, sqrt(173)/2)/(sqrt(173)/2), with S(n, x)=U(n, x/2) Chebyshev's polynomials of the second kind, A049310. S(-1, x)= 0 = U(-1, x) and T(n, x) Chebyshev's polynomials of the first kind, A053120. a(n) = 171*a(n-1) - a(n-2), n>1 ; a(0)=1, a(1)=170 . - Philippe Deléham, Nov 18 2008 EXAMPLE All positive solutions of Pell equation x^2 - 173*y^2 = -4 are (13=13*1,1), (2236=13*172,170), (382343=13*29411,29069), (65378417=13*5029109,4970629), ... MATHEMATICA LinearRecurrence[{171, -1}, {1, 170}, 20] (* G. C. Greubel, Aug 01 2019 *) PROG (PARI) my(x='x+O('x^20)); Vec((1-x)/(1-171*x+x^2)) \\ G. C. Greubel, Aug 01 2019 (MAGMA) I:=[1, 170]; [n le 2 select I[n] else 171*Self(n-1) - Self(n-2): n in [1..20]]; // G. C. Greubel, Aug 01 2019 (Sage) ((1-x)/(1-171*x+x^2)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Aug 01 2019 (GAP) a:=[1, 170];; for n in [3..20] do a[n]:=171*a[n-1]-a[n-2]; od; a; # G. C. Greubel, Aug 01 2019 CROSSREFS Sequence in context: A210784 A178499 A133328 * A250957 A114048 A187704 Adjacent sequences:  A098241 A098242 A098243 * A098245 A098246 A098247 KEYWORD nonn,easy AUTHOR Wolfdieter Lang, Sep 10 2004 STATUS approved

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Last modified December 7 09:33 EST 2019. Contains 329843 sequences. (Running on oeis4.)