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A237250 Values of x in the solutions to x^2 - 4xy + y^2 + 11 = 0, where 0 < x < y. 3
2, 3, 5, 10, 18, 37, 67, 138, 250, 515, 933, 1922, 3482, 7173, 12995, 26770, 48498, 99907, 180997, 372858, 675490, 1391525, 2520963, 5193242, 9408362, 19381443, 35112485, 72332530, 131041578, 269948677, 489053827, 1007462178, 1825173730, 3759900035 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The corresponding values of y are given by a(n+2).

Positive values of x (or y) satisfying x^2 - 14xy + y^2 + 176 = 0.

LINKS

Colin Barker, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (0,4,0,-1).

FORMULA

a(n) = 4*a(n-2)-a(n-4).

G.f.: -x*(x-1)*(x+2)*(2*x+1) / (x^4-4*x^2+1).

EXAMPLE

10 is in the sequence because (x, y) = (10, 37) is a solution to x^2 - 4xy + y^2 + 11 = 0.

PROG

(PARI) Vec(-x*(x-1)*(x+2)*(2*x+1)/(x^4-4*x^2+1) + O(x^100))

CROSSREFS

Cf. A001075, A001835, A003500, A082841.

Sequence in context: A002661 A216959 A065053 * A283314 A078715 A166874

Adjacent sequences:  A237247 A237248 A237249 * A237251 A237252 A237253

KEYWORD

nonn,easy

AUTHOR

Colin Barker, Feb 05 2014

STATUS

approved

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Last modified April 1 02:10 EDT 2020. Contains 333153 sequences. (Running on oeis4.)