A097739 Pell equation solutions (9*b(n))^2 - 82*a(n)^2 = -1 with b(n):=A097738(n), n >= 0.

1, 325, 105949, 34539049, 11259624025, 3670602893101, 1196605283526901, 390089651826876625, 127168029890278252849, 41456387654578883552149, 13514655207362825759747725, 4405736141212626618794206201, 1436256467380108914901151473801, 468215202629774293631156586252925

Offset: 0

Author

Wolfdieter Lang, Aug 31 2004

Keywords

• nonn
• easy

Examples

			(x,y) = (9*1=9;1), (2943=9*327;325), (959409=9*106601;105949), ... give the positive integer solutions to x^2 - 82*y^2 =-1.
		

Links

• Indranil Ghosh, Table of n, a(n) for n = 0..397
• Tanya Khovanova, Recursive Sequences
• Giovanni Lucca, Integer Sequences and Circle Chains Inside a Hyperbola, Forum Geometricorum (2019) Vol. 19, 11-16.
• Index entries for sequences related to Chebyshev polynomials.
• Index entries for linear recurrences with constant coefficients, signature (326,-1).

Crossrefs

Cf. A097737 for S(n, 326).

Row 9 of array A188647.

Programs

GAP

a:=[1,325];; for n in [3..20] do a[n]:=326*a[n-1]-a[n-2]; od; a; # G. C. Greubel, Aug 01 2019

Magma

I:=[1,325]; [n le 2 select I[n] else 326*Self(n-1) - Self(n-2): n in [1..20]]; // G. C. Greubel, Aug 01 2019

Mathematica

LinearRecurrence[{326, -1},{1, 325},12] (* Ray Chandler, Aug 12 2015 *)

PARI

my(x='x+O('x^20)); Vec((1-x)/(1-326*x+x^2)) \\ G. C. Greubel, Aug 01 2019

Sage

((1-x)/(1-326*x+x^2)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Aug 01 2019

Formula

a(n) = S(n, 2*163) - S(n-1, 2*163) = T(2*n+1, sqrt(82))/sqrt(82), with Chebyshev polynomials of the 2nd and first kind. See A049310 for the triangle of S(n, x)= U(n, x/2) coefficients. S(-1, x) := 0 =: U(-1, x); and A053120 for the T-triangle.

a(n) = ((-1)^n)*S(2*n, 18*i) with the imaginary unit i and Chebyshev polynomials S(n, x) with coefficients shown in A049310.

G.f.: (1-x)/(1- 326*x+x^2).

a(n) = 326*a(n-1) - a(n-2), n > 1; a(0)=1, a(1)=325. - Philippe Deléham, Nov 18 2008