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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
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.
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
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 05 2014
STATUS
approved