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 A303839 #9 May 03 2018 17:02:17 %S A303839 1,0,1,1,3,5,17,40,138,430,1546,5478,20525,77310,298301,1161692, %T A303839 4583525,18239037,73221198,296046399,1205038270,4933969005, %U A303839 20311807087,84029440358,349201537324,1457205298510,6104204225832,25661191956781,108231773165825 %N A303839 Number of noncrossing path sets on n nodes up to rotation and reflection with each path having at least two nodes. %H A303839 Andrew Howroyd, <a href="/A303839/b303839.txt">Table of n, a(n) for n = 0..200</a> %e A303839 Case n=4: There are 3 possibilities: %e A303839 . %e A303839 o---o o o o---o %e A303839 | | / %e A303839 o---o o---o o---o %e A303839 . %o A303839 (PARI) \\ See A303731 for NCPathSetsModDihedral %o A303839 Vec(NCPathSetsModDihedral(vector(30, k, k>1))) %Y A303839 Cf. A303730, A303731, A303835, A303844. %K A303839 nonn %O A303839 0,5 %A A303839 _Andrew Howroyd_, May 01 2018