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 A175005 #19 Apr 06 2018 11:43:41 %S A175005 0,1,4,13,42,137,448,1465,4790,15661,51204,167413,547362,1789617, %T A175005 5851208,19130705,62548430,204504021,668632204,2186113613,7147565882, %U A175005 23369187097,76406277968,249812682345,816770269670,2670455587581 %N A175005 Expansion of x/(1 - 4*x + 3*x^2 - 2*x^3). %C A175005 The limiting ratio a(n+1)/a(n) is 3.269530842081143.... %H A175005 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3,2). %F A175005 a(n) = 4*a(n-1) - 3*a(n-2) + 2*a(n-3), starting 0, 1, 4. %o A175005 (PARI) Vec(x/(1-4*x+3*x^2-2*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012 %Y A175005 Cf. A000045, A174631, A000931, A111285. %K A175005 nonn,easy %O A175005 0,3 %A A175005 _Roger L. Bagula_, Dec 02 2010