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 A087231 #11 Mar 16 2017 15:42:39 %S A087231 1,4,6,2,26,10,106,42,426,170,1706,682,6826,2730,27306,10922,109226, %T A087231 43690,436906,174762,1747626,699050,6990506,2796202,27962026,11184810, %U A087231 111848106,44739242,447392426,178956970,1789569706,715827882,7158278826,2863311530 %N A087231 a(n) is the smallest number such that the exponent of p=2 factor in 6*a(n)+4 equals n. %H A087231 Colin Barker, <a href="/A087231/b087231.txt">Table of n, a(n) for n = 1..1000</a> %H A087231 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,4,-4) %F A087231 For n>2, a(n) = [3/2*2^n - (-2)^n - 2]/3. - _Ralf Stephan_, May 10 2004 %F A087231 From _Colin Barker_, Mar 16 2017: (Start) %F A087231 G.f.: x*(1 + 3*x - 2*x^2 - 16*x^3 + 16*x^4) / ((1 - x)*(1 - 2*x)*(1 + 2*x)). %F A087231 a(n) = a(n-1) + 4*a(n-2) - 4*a(n-3) for n>5. %F A087231 (End) %e A087231 n = 10: m = 6*170+4 = 1024 = 2^10, so a(10) = 170. %o A087231 (PARI) Vec(x*(1 + 3*x - 2*x^2 - 16*x^3 + 16*x^4) / ((1 - x)*(1 - 2*x)*(1 + 2*x)) + O(x^40)) \\ _Colin Barker_, Mar 16 2017 %Y A087231 Cf. A085058, A087229, A087230. %K A087231 nonn,easy %O A087231 1,2 %A A087231 _Labos Elemer_, Aug 28 2003