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A199798 y-values in the solution to 17*x^2 + 16 = y^2. 5
4, 13, 21, 132, 837, 1373, 8708, 55229, 90597, 574596, 3644277, 5978029, 37914628, 240467053, 394459317, 2501790852, 15867181221, 26028336893, 165080281604, 1046993493533, 1717475775621, 10892796795012, 69085703391957, 113327372854093, 718759508189188 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
When are both n-1 and 17*n-1 perfect squares? This problem gives the equation 17*x^2+16=y^2.
LINKS
FORMULA
a(n) = 66*a(n-3) - a(n-6), a(1)=4, a(2)=13, a(3)=21, a(4)=132, a(5)=837, a(6)=1373.
G.f.: -x*(13*x^5+21*x^4+132*x^3-21*x^2-13*x-4) / (x^6-66*x^3+1). - Colin Barker, Sep 01 2013
EXAMPLE
a(7)=66*132-4=8708.
MATHEMATICA
LinearRecurrence[{0, 0, 66, 0, 0, -1}, {4, 13, 21, 132, 837, 1373}, 50]
PROG
(PARI) Vec(-x*(13*x^5+21*x^4+132*x^3-21*x^2-13*x-4)/(x^6-66*x^3+1) + O(x^100)) \\ Colin Barker, Sep 01 2013
CROSSREFS
Sequence in context: A155095 A063219 A063121 * A153193 A304905 A043469
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Nov 10 2011
EXTENSIONS
More terms from T. D. Noe, Nov 10 2011
STATUS
approved

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Last modified July 25 06:59 EDT 2024. Contains 374586 sequences. (Running on oeis4.)