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A143609
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Numerators of the upper principal and intermediate convergents to 2^(1/2).
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5
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2, 3, 10, 17, 58, 99, 338, 577, 1970, 3363, 11482, 19601, 66922, 114243, 390050, 665857, 2273378, 3880899, 13250218, 22619537, 77227930, 131836323, 450117362, 768398401, 2623476242, 4478554083, 15290740090, 26102926097, 89120964298, 152139002499
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OFFSET
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1,1
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COMMENTS
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The upper principal and intermediate convergents to 2^(1/2), beginning with
2/1, 3/2, 10/7, 17/12, 58/41, form a strictly decreasing sequence;
essentially, numerators=A143609 and denominators=A084068.
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REFERENCES
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Serge Lang, Introduction to Diophantine Approximations, Addison-Wesley, New York, 1966.
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LINKS
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Colin Barker, Table of n, a(n) for n = 1..1000
Creighton Kenneth Dement, Comments on A143608 and A143609
Clark Kimberling, Best lower and upper approximates to irrational numbers, Elemente der Mathematik, 52 (1997) 122-126.
Index entries for linear recurrences with constant coefficients, signature (0,6,0,-1).
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FORMULA
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a(n) = 6 * a(n-2) - a(n-4). a(2*n) = A001541(n) if n>0. a(2*n + 1) = 2 * A001653(n + 1).- Michael Somos, Sep 03 2013
G.f.: x * (2 + 3*x - 2*x^2 - x^3) / (1 - 6*x^2 + x^4). - Michael Somos, Sep 03 2013
a(n) = (2+sqrt(2)+(-1)^n*(-2+sqrt(2)))*((-1+sqrt(2))^n+(1+sqrt(2))^n)/(4*sqrt(2)). - Colin Barker, Mar 27 2016
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EXAMPLE
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2*x + 3*x^2 + 10*x^3 + 17*x^4 + 58*x^5 + 99*x^6 + 338*x^7 + 577*x^8 + ...
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MATHEMATICA
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Rest@ CoefficientList[Series[x (2 + 3 x - 2 x^2 - x^3)/(1 - 6 x^2 + x^4), {x, 0, 30}], x] (* Michael De Vlieger, Mar 27 2016 *)
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PROG
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(PARI) {a(n) = if( n<1, 0, polcoeff( x * (2 + 3*x - 2*x^2 - x^3) / (1 - 6*x^2 + x^4) + x * O(x^n), n))} /* Michael Somos, Sep 03 2013 */
(PARI) x='x+O('x^99); Vec(x*(2+3*x-2*x^2-x^3)/(1-6*x^2+x^4)) \\ Altug Alkan, Mar 27 2016
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CROSSREFS
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Cf. A001541, A001653, A010914, A084068.
Sequence in context: A213391 A300285 A192798 * A066915 A070253 A147673
Adjacent sequences: A143606 A143607 A143608 * A143610 A143611 A143612
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KEYWORD
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nonn,easy
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AUTHOR
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Clark Kimberling, Aug 27 2008
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STATUS
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approved
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