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 A209026 #10 Mar 20 2017 09:51:06 %S A209026 1,2,2,6,11,33,86,278,873,2938,9904,34321,119673,422725,1502590, %T A209026 5381671,19377063,70138385,254978018,930709334,3409356533,12530190100, %U A209026 46188325542,170723964752,632624262841,2349655631568,8745690221340,32617408075856 %N A209026 Number of n-bead necklaces labeled with numbers -2..2 allowing reversal, with sum zero and first differences in -2..2. %H A209026 Andrew Howroyd, <a href="/A209026/b209026.txt">Table of n, a(n) for n = 1..100</a> %e A209026 Some solutions for n=6: %e A209026 ..0...-1...-1...-2...-2...-2...-1...-1...-2...-1...-1...-1...-2...-1...-1...-1 %e A209026 ..0....0....0....0....0...-1...-1...-1...-1...-1...-1....0...-1...-1....0....0 %e A209026 ..0....0....0....1....0....1....0....0....1...-1....1....1....1....0...-1....1 %e A209026 ..0....1....0....0....1....0....0....0....2....1....0...-1....1....1....0...-1 %e A209026 ..0...-1....0....1....1....2....1....2....1....1....0....0....1....0....2....1 %e A209026 ..0....1....1....0....0....0....1....0...-1....1....1....1....0....1....0....0 %Y A209026 Column 2 of A209032. %K A209026 nonn %O A209026 1,2 %A A209026 _R. H. Hardin_, Mar 04 2012 %E A209026 a(22)-a(28) from _Andrew Howroyd_, Mar 19 2017