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 A208818 #6 Mar 12 2017 23:16:06 %S A208818 1,2,2,5,7,18,32,84,185,486,1192,3179,8261,22290,59788,163181,445699, %T A208818 1228686,3396224,9440759,26322371,73680058,206822134,582308320, %U A208818 1643573625,4650401810,13186590962,37469003353 %N A208818 Number of n-bead necklaces labeled with numbers -1..1 allowing reversal, with sum zero. %C A208818 Column 1 of A208825. %e A208818 All solutions for n=3: %e A208818 ..0...-1 %e A208818 ..0....0 %e A208818 ..0....1 %K A208818 nonn %O A208818 1,2 %A A208818 _R. H. Hardin_, Mar 01 2012