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 A131508 #9 Oct 24 2018 22:53:32 %S A131508 0,0,0,2,1,1,1,4,2,2,2,6,3,3,3,8,4,4,4,10,5,5,5,12,6,6,6,14,7,7,7,16, %T A131508 8,8,8,18,9,9,9,20,10,10,10,22,11,11,11,24,12,12,12,26,13,13,13,28,14, %U A131508 14,14,30,15,15,15,32,16,16,16,34,17,17,17,36,18,18,18,38,19,19,19,40,20 %N A131508 2*A000027 (natural numbers) sandwiched by tripled A001477 (nonnegative numbers). %H A131508 Muniru A Asiru, <a href="/A131508/b131508.txt">Table of n, a(n) for n = 0..5000</a> %F A131508 From _Chai Wah Wu_, Oct 24 2018: (Start) %F A131508 a(n) = 2*a(n-4) - a(n-8) for n > 7. %F A131508 G.f.: x^3*(x^3 + x^2 + x + 2)/(x^8 - 2*x^4 + 1). (End) %p A131508 seq(coeff(series(x^3*(x^3+x^2+x+2)/(x^8-2*x^4+1),x,n+1), x, n), n = 0 .. 85); # _Muniru A Asiru_, Oct 24 2018 %o A131508 (GAP) a:=[0,0,0,2,1,1,1,4];; for n in [9..85] do a[n]:=2*a[n-4]-a[n-8]; od; a; # _Muniru A Asiru_, Oct 24 2018 %K A131508 nonn,easy,less %O A131508 0,4 %A A131508 _Paul Curtz_, Aug 13 2007