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 A208819 #6 Mar 12 2017 23:16:35 %S A208819 1,3,5,16,45,167,609,2471,10143,43223,186533,818836,3629835,16250859, %T A208819 73300289,332895316,1520604469,6981991345,32205476541 %N A208819 Number of n-bead necklaces labeled with numbers -2..2 allowing reversal, with sum zero. %C A208819 Column 2 of A208825. %e A208819 All solutions for n=3: %e A208819 .-2...-1...-1...-2....0 %e A208819 ..1....0...-1....0....0 %e A208819 ..1....1....2....2....0 %K A208819 nonn %O A208819 1,2 %A A208819 _R. H. Hardin_, Mar 01 2012