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 A018840 #29 Jan 05 2018 07:35:31
%S A018840 0,5,4,5,2,5,2,5,4,5,4,7,4,5,6,7,6,7,6,7,8,9,8,9,8,9,10,11,10,11,10,
%T A018840 11,12,13,12,13,12,13,14,15,14,15,14,15,16,17,16,17,16,17,18,19,18,19,
%U A018840 18,19,20,21,20,21,20,21,22,23,22,23,22,23,24,25,24,25,24,25,26,27,26,27,26,27
%N A018840 Number of steps for {2,3} fairy knight to reach (n,0) on infinite chessboard.
%C A018840 This piece is also known as a (2,3)-leaper or a zebra. - _Franklin T. Adams-Watters_, Dec 27 2017
%C A018840 Apparently also the minimum number of moves of the (1,5)-leaper to reach (n,n) starting from (0,0). - _R. J. Mathar_, Jan 05 2018
%H A018840 Colin Barker, <a href="/A018840/b018840.txt">Table of n, a(n) for n = 0..1000</a>
%H A018840 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,1,-1)
%F A018840 For n >= 18, a(n) = a(n-6) + 2. - _David W. Wilson_
%F A018840 From _Colin Barker_, Dec 28 2017: (Start)
%F A018840 G.f.: x*(5 - x + x^2 - 3*x^3 + 3*x^4 - 3*x^5 - 2*x^6 + 2*x^9 - 2*x^12 + 2*x^13 - 2*x^16 + 2*x^17) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).
%F A018840 a(n) = a(n-1) + a(n-6) - a(n-7) for n>7.
%F A018840 (End)
%F A018840 3*a(n) = A004442(n+3)-A084100(n), n>11. - _R. J. Mathar_, Jan 02 2018
%o A018840 (PARI) concat(0, Vec(x*(5 - x + x^2 - 3*x^3 + 3*x^4 - 3*x^5 - 2*x^6 + 2*x^9 - 2*x^12 + 2*x^13 - 2*x^16 + 2*x^17) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)) + O(x^100))) \\ _Colin Barker_, Dec 28 2017
%K A018840 nonn,easy
%O A018840 0,2
%A A018840 _Marc LeBrun_