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A201157 y-values in the solution to 5*x^2 - 20 = y^2. 2
0, 5, 15, 40, 105, 275, 720, 1885, 4935, 12920, 33825, 88555, 231840, 606965, 1589055, 4160200, 10891545, 28514435, 74651760, 195440845, 511670775, 1339571480, 3507043665, 9181559515, 24037634880, 62931345125, 164756400495, 431337856360, 1129257168585 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Except a(1), the same as A054888. - R. J. Mathar, Nov 28 2011

LINKS

Table of n, a(n) for n=1..29.

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

FORMULA

a(n) = 3*a(n-1) - a(n-2), n>2.

G.f.: 5*x^2 / (x^2 - 3*x + 1). - Colin Barker, Apr 08 2013

a(n) = 5*Fibonacci(2*n-2) = Lucas(2*n-1) + Lucas(2*n-3) with Lucas(-1) = -1. - Bruno Berselli, Feb 15 2017

EXAMPLE

15 is in the sequence because 15^2 = 5*7^2 - 20.

MATHEMATICA

LinearRecurrence[{3, -1}, {0, 5}, 50]

CROSSREFS

Cf. A000032, A005248.

Sequence in context: A000333 A291225 A054888 * A301980 A230955 A038066

Adjacent sequences:  A201154 A201155 A201156 * A201158 A201159 A201160

KEYWORD

nonn,easy

AUTHOR

Sture Sjöstedt, Nov 27 2011

EXTENSIONS

More terms from Colin Barker, Apr 08 2013

STATUS

approved

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Last modified June 7 02:48 EDT 2020. Contains 334836 sequences. (Running on oeis4.)