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 A249998 #8 Jun 13 2015 00:55:18 %S A249998 1,0,13,12,169,312,2341,6084,34177,107184,517309,1803516,8011225, %T A249998 29653416,125788117,481629108,1991086513,7770635808,31663673965, %U A249998 124911303660,504875391241,2003811035160,8062315730053,32108048151972,128855836912609,514152414736272,2060422457687581 %N A249998 Expansion of 1/((1+x)*(1+3*x)*(1-4*x)). %H A249998 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,13,12). %F A249998 a(n) = (-1)^n*3^(n+2)/14 + 4^(n+2)/35 - (-1)^n/10. - _R. J. Mathar_, Jan 09 2015 %Y A249998 Cf. A016208, A099621, A249997. %K A249998 nonn,easy %O A249998 0,3 %A A249998 _Alex Ratushnyak_, Dec 28 2014