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 A235389 #29 Nov 13 2014 17:31:20 %S A235389 22,9482,112269228,37515056726494,355023905438833546724 %N A235389 Number of paths joining opposite corners of an n X n grid with every vertex appearing at most twice in the path. %e A235389 The 22 paths in a 2 X 2 grid whose nodes are numbered from 1 to 4 in the natural way are 124, 134, 12124, 12134, 12424, 12434, 13124, 13134, 13424, 13434, 1212434, 1213424, 1213434, 1242134, 1243124, 1243134, 1312424, 1312434, 1313424, 1342124, 1342134, 1343124. - _Giovanni Resta_, Mar 24 2014 %Y A235389 Cf. A007764, A239688. %K A235389 nonn,more %O A235389 2,1 %A A235389 _Muhammad Kholilurrohman_, Jan 09 2014 %E A235389 a(5)-a(6) from _Muhammad Kholilurrohman_, Nov 13 2014