This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A041065 #23 Jul 09 2025 00:13:03
%S A041065 1,4,49,200,2449,9996,122401,499600,6117601,24970004,305757649,
%T A041065 1248000600,15281764849,62375059996,763782484801,3117504999200,
%U A041065 38173842475201,155812874900004,1907928341275249,7787526240001000,95358243221287249,389220499125149996
%N A041065 Denominators of continued fraction convergents to sqrt(39).
%H A041065 Vincenzo Librandi, <a href="/A041065/b041065.txt">Table of n, a(n) for n = 0..200</a>
%H A041065 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (0,50,0,-1).
%F A041065 G.f.: -(x^2-4*x-1) / (x^4-50*x^2+1). - _Colin Barker_, Nov 12 2013
%F A041065 a(n) = 50*a(n-2) - a(n-4). - _Vincenzo Librandi_, Dec 10 2013
%t A041065 Table[Denominator[FromContinuedFraction[ContinuedFraction[Sqrt[39], n]]], {n, 1, 50}] (* _Vladimir Joseph Stephan Orlovsky_, Mar 21 2011 *)
%t A041065 Denominator[Convergents[Sqrt[39], 30]] (* _Vincenzo Librandi_, Dec 10 2013 *)
%o A041065 (Magma) I:=[1, 4, 49, 200]; [n le 4 select I[n] else 50*Self(n-2)-Self(n-4): n in [1..30]]; // _Vincenzo Librandi_, Dec 10 2013
%Y A041065 Cf. A010493, A041064.
%K A041065 nonn,cofr,frac,easy
%O A041065 0,2
%A A041065 _N. J. A. Sloane_
%E A041065 More terms from _Colin Barker_, Nov 12 2013