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 A209027 #11 Mar 20 2017 09:51:08 %S A209027 1,2,4,12,34,144,576,2613,11841,55773,265095,1280476,6238246,30674021, %T A209027 151874427,756842052,3792315084,19096602857,96586072494,490453174481, %U A209027 2499410534082,12778951549191,65530990963959,336965088080673,1737060054201011,8975377470866966 %N A209027 Number of n-bead necklaces labeled with numbers -3..3 allowing reversal, with sum zero and first differences in -3..3. %H A209027 Andrew Howroyd, <a href="/A209027/b209027.txt">Table of n, a(n) for n = 1..100</a> %e A209027 Some solutions for n=6: %e A209027 .-2...-3...-3...-3...-2...-1...-1...-3...-3...-3...-2...-1...-3...-1...-1...-1 %e A209027 ..0...-2...-1...-2...-1...-1....1....0....0...-1....0....0...-2...-1...-1...-1 %e A209027 ..0....1....1....1....0....2...-1...-1....0....0....2...-1....1...-1....0....0 %e A209027 ..2....2....2....1....0...-1....1....2....0....2....0....0....3....2....1...-1 %e A209027 ..0....2....1....3....3...-1...-1....2....3....2...-1....0....2...-1....1....2 %e A209027 ..0....0....0....0....0....2....1....0....0....0....1....2...-1....2....0....1 %Y A209027 Column 3 of A209032. %K A209027 nonn %O A209027 1,2 %A A209027 _R. H. Hardin_, Mar 04 2012 %E A209027 a(19)-a(26) from _Andrew Howroyd_, Mar 19 2017