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 A094025 #14 Jun 13 2015 00:51:20 %S A094025 1,3,4,12,13,39,40,120,121,363,364,1092,1093,3279,3280,9840,9841, %T A094025 29523,29524,88572,88573,265719,265720,797160,797161,2391483,2391484, %U A094025 7174452,7174453,21523359,21523360,64570080,64570081,193710243,193710244 %N A094025 Expansion of (1+3x)/((1-x^2)(1-3x^2)). %C A094025 Add 1, triple, add 1, triple, ... (of course this is simply a restatement of one of _Philippe Deléham_'s formulas). - _Jon Perry_, Aug 11 2014 %H A094025 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-3). %F A094025 a(n)=4a(n-2)-3a(n-4); a(n)=3*3^(n/2)(1/4+sqrt(3)/4+(1/4-sqrt(3)/4)(-1)^n)+(-1)^n/2-1. %F A094025 a(n) = a(n-1)*3 if n odd; a(n) = a(n-1)+1 if n even. - _Philippe Deléham_, Apr 22 2013 %F A094025 a(2n) = A003462(n+1); a(2n+1) = A123109(n+1) = A029858(n+1). - _Philippe Deléham_, Apr 22 2013 %Y A094025 Cf. A075427, A080610, A083416. %K A094025 easy,nonn %O A094025 0,2 %A A094025 _Paul Barry_, Apr 22 2004