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 A246536 #9 Sep 06 2014 01:39:35 %S A246536 3,25,1885,3636297,327094648711 %N A246536 a(n) = number of strings (including the empty string) over an alphabet of size n that do not have any substrings of length > 1 that appear more than once in the string. %C A246536 Here "substrings" have no "gaps", i.e. a substring means a subsequence of characters from the original string using contiguous indices. %C A246536 The number of De Bruijn sequences B(n,2) (which has a known explicit formula) can be used to give the fairly tight lower bound that a(n) > 2*n^2*B(n,2). See A166315. %Y A246536 Cf. A166315. %K A246536 nonn,more %O A246536 1,1 %A A246536 _Peter M. Huggins_, Aug 28 2014