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 A097838 First differences of Chebyshev polynomials S(n,51) = A097836(n) with Diophantine property. 5
 1, 50, 2549, 129949, 6624850, 337737401, 17217982601, 877779375250, 44749530155149, 2281348258537349, 116304011655249650, 5929223246159194801, 302274081542463685201, 15410048935419488750450, 785610221624851462587749 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS (7*b(n))^2 - 53*a(n)^2 = -4 with b(n)=A097837(n) give all positive solutions of this Pell equation. LINKS Indranil Ghosh, Table of n, a(n) for n = 0..584 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 (51, -1). FORMULA a(n) = ((-1)^n)*S(2*n, 7*i) with the imaginary unit i and the S(n, x) = U(n, x/2) Chebyshev polynomials. G.f.: (1-x)/(1 - 51*x + x^2). a(n) = S(n, 51) - S(n-1, 51) = T(2*n+1, sqrt(53)/2)/(sqrt(53)/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) = 51*a(n-1) - a(n-2), a(0)=1, a(1)=50. - Philippe Deléham, Nov 18 2008 EXAMPLE All positive solutions of Pell equation x^2 - 53*y^2 = -4 are (7=7*1,1), (364=7*52,50), (18557=7*2651,2549), (946043=7*135149,129949), ... MATHEMATICA LinearRecurrence[{51, -1}, {1, 50}, 20] (* G. C. Greubel, Jan 13 2019 *) PROG (PARI) my(x='x+O('x^20)); Vec((1-x)/(1-51*x+x^2)) \\ G. C. Greubel, Jan 13 2019 (MAGMA) m:=20; R:=PowerSeriesRing(Integers(), m); Coefficients(R!( (1-x)/(1-51*x+x^2) )); // G. C. Greubel, Jan 13 2019 (Sage) ((1-x)/(1-51*x+x^2)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Jan 13 2019 (GAP) a:=[1, 50];; for n in [3..20] do a[n]:=51*a[n-1]-a[n-2]; od; a; # G. C. Greubel, Jan 13 2019 CROSSREFS Sequence in context: A223796 A165800 A042201 * A203842 A251058 A239653 Adjacent sequences:  A097835 A097836 A097837 * A097839 A097840 A097841 KEYWORD nonn,easy AUTHOR Wolfdieter Lang, Sep 10 2004 STATUS approved

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Last modified October 19 12:10 EDT 2019. Contains 328219 sequences. (Running on oeis4.)