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 A063888 #8 Apr 19 2019 09:30:21 %S A063888 1,6,30,180,1026,6156,35940,215640,1271106,7626636,45182124,271092744, %T A063888 1610875836,9665255016,57546367704,345278206224,2058613385346, %U A063888 12351680312076,73717606430364,442305638582184,2641804748619732 %N A063888 Number of n-step walks on a cube lattice starting from the origin but not returning to it at any stage. %C A063888 a(n)/6^n tends to 0.65946... %D A063888 Steven R. Finch, Mathematical Constants, Cambridge, 2003, pp. 322-331. %H A063888 Steven R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/constant/polya/polya.html">Polya's Random Walk Constants</a> [Broken link] %H A063888 Steven R. Finch, <a href="http://web.archive.org/web/20010603070928/http://www.mathsoft.com/asolve/constant/polya/polya.html">Polya's Random Walk Constants</a> [From the Wayback machine] %F A063888 a(2n) = 6*a(2n-1)-A049037(n); a(2n+1) = 6*a(2n). %e A063888 a(2) = 30 since there are 36 2-step walks but 6 of them involve a return to the origin at some stage; similarly a(3) = 180 since there are 216 3-step walks but 36 of them involve a return to the origin at some stage. %K A063888 nonn %O A063888 0,2 %A A063888 _Henry Bottomley_, Aug 28 2001