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 A215070 #9 Dec 11 2015 21:39:11 %S A215070 1,1,2,4,12,40,154,660,3114,15930,87645,514851,3211220,21166029, %T A215070 146849903,1068808441,8136559688,64621235409,534207882566 %N A215070 Number of squarefree words of length n in an n-ary alphabet, with new values 0..n-1 introduced in increasing order. %C A215070 Diagonal of A215075. %e A215070 Some solutions for n=6: %e A215070 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 %e A215070 ..1....1....1....1....1....1....1....1....1....1....1....1....1....1....1....1 %e A215070 ..2....2....2....0....0....2....2....0....2....0....0....2....2....0....2....2 %e A215070 ..1....1....3....2....2....0....3....2....3....2....2....3....3....2....1....1 %e A215070 ..0....0....0....3....1....1....4....3....4....0....3....2....1....3....0....3 %e A215070 ..1....3....2....0....0....3....5....4....0....1....2....0....2....1....2....4 %K A215070 nonn %O A215070 1,3 %A A215070 _R. H. Hardin_, Aug 02 2012