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 A078702 #9 Mar 11 2025 13:18:01 %S A078702 1,2,13,213,7584,454380,39665160,4775586480,756765576000, %T A078702 152553490810560,38148245068953600,11587644586640707200, %U A078702 4202354709635579481600,1793612851748170637184000,889985376998423302704307200,508018135094443467957310848000,330553193467656241628008759296000 %N A078702 Number of ways to lace a shoe that has n pairs of eyelets such that each eyelet has at least one direct connection to the opposite side. %C A078702 The lace is "undirected": reversing the order of eyelets along the path does not count as a different solution. It must begin and end at the extreme pair of eyelets, %H A078702 <a href="/index/La#lacings">Index entries for sequences related to shoe lacings</a> %F A078702 a(n) = (A078698(n) + A078700(n))/2. %e A078702 a(3) = 13: label the eyelets 1,2,3 from front to back on the left side then 4,5,6 from back to front on the right side. The lacings are: 124356 154326 153426 142536 145236 135246 125346 124536 125436 152346 153246 152436 154236. %Y A078702 Cf. A078698, A078700, A078675. %K A078702 nonn %O A078702 1,2 %A A078702 _Hugo Pfoertner_, Dec 18 2002 %E A078702 More terms from _Hugo Pfoertner_, Mar 11 2025