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 A154023 #33 Jan 03 2024 23:46:42
%S A154023 0,6,216,7770,279504,10054374,361677960,13010352186,468011000736,
%T A154023 16835385674310,605605873274424,21784976052204954,783653532006103920,
%U A154023 28189742176167536166,1014047064810025198056,36477504590984739593850
%N A154023 a(n+2) = 36*a(n+1) - a(n), a(1)=0, a(2)=6.
%C A154023 If a(n)=x and a(n+1)=y then (x^2+y^2)/(xy+1)=36.
%H A154023 Vincenzo Librandi, <a href="/A154023/b154023.txt">Table of n, a(n) for n = 1..500</a>
%H A154023 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (36,-1).
%F A154023 From _R. J. Mathar_, Oct 18 2010: (Start)
%F A154023 a(n)= +36*a(n-1) -a(n-2)
%F A154023 a(n) = 6*A144128(n-1).
%F A154023 G.f.: 6*x/(1 -36*x +x^2). (End)
%t A154023 LinearRecurrence[{36,-1},{0,6},50] (* _Vincenzo Librandi_, Jan 30 2012 *)
%o A154023 (PARI) concat(0,Vec(6/(1-36*x+x^2)+O(x^98))) \\ _Charles R Greathouse IV_, Dec 27 2011
%Y A154023 Cf. A065100, A154021-A154027.
%K A154023 nonn,easy
%O A154023 1,2
%A A154023 _Vincenzo Librandi_, Jan 04 2009
%E A154023 Edited by _N. J. A. Sloane_, Jun 23 2010 at the suggestion of _Joerg Arndt_.
%E A154023 Missing digit inserted in a(8) by _R. J. Mathar_, Oct 18 2010