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%I #17 Sep 08 2022 08:44:54
%S 20,21,860,881,36100,36981,1515340,1552321,63608180,65160501,
%T 2670028220,2735188721,112077577060,114812765781,4704588208300,
%U 4819400974081,197480627171540,202300028145621,8289481752996380
%N Numerators of continued fraction convergents to sqrt(440).
%H Vincenzo Librandi, <a href="/A041838/b041838.txt">Table of n, a(n) for n = 0..200</a>
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (0,42,0,-1).
%F G.f.: (20 + 21*x + 20*x^2 - x^3)/(1 - 42*x^2 + x^4). - _Vincenzo Librandi_, Nov 10 2013
%F a(n) = 42*a(n-2) - a(n-4). - _Vincenzo Librandi_, Nov 10 2013
%t Numerator[Convergents[Sqrt[440], 30]] (* or *) CoefficientList[Series[(20 + 21 x + 20 x^2 - x^3)/(1 - 42 x^2 + x^4), {x, 0, 25}], x] (* _Vincenzo Librandi_, Nov 10 2013 *)
%o (Magma) I:=[20,21,860,881]; [n le 8 select I[n] else 42*Self(n-2)-Self(n-4): n in [1..25]]; // _Vincenzo Librandi_, Nov 10 2013
%Y Cf. A041839.
%K nonn,cofr,frac,easy,less
%O 0,1
%A _N. J. A. Sloane_.
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