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%I #25 Sep 08 2022 08:44:53
%S 1,2,25,52,649,1350,16849,35048,437425,909898,11356201,23622300,
%T 294823801,613269902,7654062625,15921395152,198710804449,413343004050,
%U 5158826853049,10730996710148,133930787374825,278592571459798,3477041644892401,7232675861244600
%N Denominators of continued fraction convergents to sqrt(42).
%H Vincenzo Librandi, <a href="/A041071/b041071.txt">Table of n, a(n) for n = 0..200</a>
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,26,0,-1).
%F G.f.: -(x^2-2*x-1) / (x^4-26*x^2+1). - _Colin Barker_, Nov 12 2013
%F a(n) = 26*a(n-2) - a(n-4). - _Vincenzo Librandi_, Dec 10 2013
%t Table[Denominator[FromContinuedFraction[ContinuedFraction[Sqrt[42],n]]],{n,1,50}] (* _Vladimir Joseph Stephan Orlovsky_, Mar 22 2011 *)
%t Denominator[Convergents[Sqrt[42], 30]] (* _Vincenzo Librandi_, Dec 10 2013 *)
%t LinearRecurrence[{0,26,0,-1},{1,2,25,52},30] (* _Harvey P. Dale_, Oct 17 2019 *)
%o (Magma) I:=[1, 2, 25, 52]; [n le 4 select I[n] else 26*Self(n-2)-Self(n-4): n in [1..30]]; // _Vincenzo Librandi_, Dec 10 2013
%Y Cf. A041070.
%K nonn,cofr,easy
%O 0,2
%A _N. J. A. Sloane_.
%E More terms from _Colin Barker_, Nov 12 2013
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