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 A236753 #35 Jun 10 2017 22:34:06 %S A236753 1,28,653,28512,3060417,873239772,687430009069,1532025110398168, %T A236753 9829526954625359697,183563561823425961932572, %U A236753 10056737067604248527218979485,1626248896102138091401810358337184 %N A236753 Number of simple (non-intersecting) directed paths on the grid graph P_n X P_n. %C A236753 This is the number of directed paths on P_n X P_n of any length and also includes one zero length path per vertex. - _Andrew Howroyd_, May 27 2017 %F A236753 a(n) = 2*A288032(n) + n^2. - _Andrew Howroyd_, Jun 10 2017 %e A236753 For n=2 there are 4 zero length paths (one for each vertex), 8 paths with 1 one edge, 8 paths with 2 edges and 8 paths with 3 edges, so a(2)=28. - _Andrew Howroyd_, May 27 2017 %Y A236753 Cf. A236690 (includes diagonal edges). %Y A236753 Cf. A288032, A007764, A121785, A120443. %K A236753 nonn,hard,more %O A236753 1,2 %A A236753 _Jaimal Ichharam_, Jan 30 2014 %E A236753 a(6) corrected and a(8) added from _Jaimal Ichharam_, Feb 13 2014 %E A236753 a(6)-a(8) corrected and a(9)-a(12) from _Andrew Howroyd_, May 27 2017