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 A138569 #8 Jul 28 2015 15:52:43 %S A138569 0,1,0,1,0,1,1,0,4,-2,10,-4,20,-4,36,0,64,8,120,16,240,16,496,0,1024, %T A138569 -32,2080,-64,4160,-64,8256,0,16384,128,32640,256,65280,256,130816,0, %U A138569 262144,-512,524800,-1024,1049600,-1024,2098176,0,4194304,2048,8386560,4096,16773120 %N A138569 First differences of A137776. %H A138569 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0, 4, 0, -6, 0, 4). %F A138569 a(n)=4a(n-2)-6a(n-4)+4a(n-6), n>7. %F A138569 a(2n)=A000749(n). a(2n+1)=(-1)^(n+1)*A009116(n-1), n>0. %F A138569 O.g.f.: x(1-x)(x^4-2x^2+1+x-2x^3+2x^5)/((1-2x^2)(1-2x^2+2x^4)). - _R. J. Mathar_, Aug 02 2008 %Y A138569 Cf. A135356. %K A138569 sign %O A138569 0,9 %A A138569 _Paul Curtz_, May 12 2008 %E A138569 Edited and extended by _R. J. Mathar_, Aug 02 2008