OFFSET

1,1

COMMENTS

Here "substrings" have no "gaps", i.e. a substring means a subsequence of characters from the original string using contiguous indices.

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.

CROSSREFS

KEYWORD

nonn,more

AUTHOR

Peter M. Huggins, Aug 28 2014

STATUS

approved