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 A216241 #31 May 19 2019 20:35:23
%S A216241 1,2,4,8,16,32,62,124,236,472,890,1780,3340,6680,12502,25004,46732,
%T A216241 93464,174554,349108,651740,1303480,2432918,4865836,9080956,18161912,
%U A216241 33892954,67785908,126494956,252989912,472095062,944190124,1761901676,3523803352,6575544410,13151088820
%N A216241 Number of n-step walks (each step +-1 starting from 0) which are never more than 5 or less than -5.
%F A216241 a(n) = A068913(5,n).
%F A216241 a(n) = 6*a(n-2) - 9*a(n-4) + 2*a(n-6).
%F A216241 a(n) = 2^n for n < 6.
%F A216241 G.f.: ((1-x)^2*(1+x)^2*(1+2*x)) / ((1-2*x^2)*(1-4*x^2+x^4)).
%F A216241 a(2*n+1) = 2*a(2*n).
%F A216241 a(n) = Sum_{k=0..n} A214846(n-k, k). - _Philippe Deléham_, Mar 25 2013
%t A216241 nn=35;CoefficientList[Series[(1+2x)(1-x^2)^2/(1-6x^2+9x^4-2x^6),{x,0,nn}],x] (* _Geoffrey Critzer_, Jan 14 2014 *)
%Y A216241 Cf. Rows of A068913: A000007, A016116 (without initial term), A068911, A068912, A214846, A216212.
%K A216241 nonn,walk,easy
%O A216241 0,2
%A A216241 _Philippe Deléham_, Mar 15 2013
%E A216241 a(34) corrected by _Sean A. Irvine_, May 19 2019