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A158656 a(n) = 54*n^2 - 1. 2
53, 215, 485, 863, 1349, 1943, 2645, 3455, 4373, 5399, 6533, 7775, 9125, 10583, 12149, 13823, 15605, 17495, 19493, 21599, 23813, 26135, 28565, 31103, 33749, 36503, 39365, 42335, 45413, 48599, 51893, 55295, 58805, 62423, 66149, 69983 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (54*n^2 - 1)^2 - (729*n^2 - 27)*(2*n)^2 = 1 can be written as a(n)^2 - A158655(n)*A005843(n)^2 = 1.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Vincenzo Librandi, X^2-AY^2=1

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

G.f.: x*(-53 - 56*x + x^2)/(x-1)^3.

a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).

MATHEMATICA

LinearRecurrence[{3, -3, 1}, {53, 215, 485}, 50] (* Vincenzo Librandi, Feb 17 2012 *)

54*Range[40]^2-1 (* Harvey P. Dale, Sep 15 2021 *)

PROG

(Magma) I:=[53, 215, 485]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 17 2012

(PARI) for(n=1, 40, print1(54*n^2 - 1", ")); \\ Vincenzo Librandi, Feb 17 2012

CROSSREFS

Cf. A005843, A158655.

Sequence in context: A330810 A005146 A158644 * A013536 A142000 A053652

Adjacent sequences: A158653 A158654 A158655 * A158657 A158658 A158659

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Mar 23 2009

EXTENSIONS

Comment rephrased and redundant formula replaced by R. J. Mathar, Oct 19 2009

STATUS

approved

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Last modified February 6 20:45 EST 2023. Contains 360111 sequences. (Running on oeis4.)