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A097314 Pell equation solutions (3*a(n))^2 - 10*b(n)^2 = -1 with b(n) = A097315(n), n>=0. 5
1, 39, 1481, 56239, 2135601, 81096599, 3079535161, 116941239519, 4440687566561, 168629186289799, 6403468391445801, 243163169688650639, 9233796979777278481, 350641122061847931639, 13315128841370444123801, 505624254850015028772799, 19200406555459200649242561, 729109824852599609642444519, 27686972937843325965763649161 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Indranil Ghosh, Table of n, a(n) for n = 0..631

Tanya Khovanova, Recursive Sequences

Index entries for sequences related to Chebyshev polynomials.

Index entries for linear recurrences with constant coefficients, signature (38, -1).

FORMULA

a(n) = S(n, 38) + S(n-1, 38) = S(2*n, 2*sqrt(10)), with Chebyshev polynomials of the second kind. See A049310 for the triangle of S(n, x) = U(n, x/2) coefficients. S(-1, x) := 0 =: U(-1, x).

a(n) = (-1)^n*T(2*n+1, 3*I)/(3*I) with the imaginary unit I and Chebyshev polynomials of the first kind. See the T-triangle A053120.

G.f.: (1+x)/(1-38*x+x^2).

a(n) = ((3+sqrt(10))*(19+6*sqrt(10))^n-((-3+sqrt(10))*(19-6*sqrt(10))^n))/6. - Gerry Martens, Jul 09 2015

EXAMPLE

(x,y) = (3,1), (117,37), (4443,1405), ... give the positive integer solutions to x^2 - 10*y^2 = -1.

MATHEMATICA

LinearRecurrence[{38, -1}, {1, 39}, 15] (* Ray Chandler, Aug 11 2015 *)

PROG

(PARI) Vec((1+x)/(1-38*x+x^2) + O(x^20)) \\ Michel Marcus, Jul 10 2015

(MAGMA) [Round(((3+Sqrt(10))*(19+6*Sqrt(10))^n-((-3+Sqrt(10))*(19-6*Sqrt(10))^n))/6): n in [1..20]]; // Vincenzo Librandi, Jul 10 2015

CROSSREFS

Cf. A078987 for S(n, 38).

Sequence in context: A078970 A020303 A235973 * A162871 A163222 A163668

Adjacent sequences:  A097311 A097312 A097313 * A097315 A097316 A097317

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang, Aug 31 2004

EXTENSIONS

More terms from Indranil Ghosh, Feb 04 2017

STATUS

approved

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Last modified June 24 16:32 EDT 2017. Contains 288707 sequences.