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 A337901 #4 Sep 29 2020 07:50:06 %S A337901 1,25,441,7056,108900,1656369,25050025,378224704,5712638724, %T A337901 86394844900,1308887012356,19868414760000,302198588499600, %U A337901 4605510959127225,70321771565375625,1075697380745222400,16483023079048102500,252980753801047064100,3888662839165553120100 %N A337901 The number of walks of length 2n+1 on the square lattice that start from the origin (0,0) and end at the vertex (3,0). %F A337901 a(n) = [A002054(n)]^2. %F A337901 G.f.: x*4F3(2,2,5/2,5/2; 1,4,4; 16*x). %F A337901 D-finite with recurrence (n+2)^2*(n-1)^2*a(n) -4*n^2*(2*n+1)^2*a(n-1)=0. %Y A337901 Cf. A002894 (end at (0,0)), A060150 (end at (1,0)), A135389 (end at (1,1)), A337900 (at (2,0)), A337902 (at(2,1)) %K A337901 nonn,easy,walk %O A337901 1,2 %A A337901 _R. J. Mathar_, Sep 29 2020