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 A075100 #15 Nov 11 2024 09:00:58 %S A075100 0,0,3,4,10,11 %N A075100 Number of words of length strictly between 1 and n that are needed on the way to computing all words of length n in the free monoid with two generators. %C A075100 I believe a(2n) = a(n) + 2^n. I think a(7) = 28. %C A075100 _Benoit Jubin_ (Jan 24 2009) suggests replacing "monoid" in the definition by "semigroup" and remarks that it makes sense to introduce a new sequence that includes words of length 1 in the count. %e A075100 a(3) = 3 because we need only xx, xy, yy to generate each of xxx, xxy, xyx, yxx, xyy, yxy, yyx, yyy. %Y A075100 Cf. A075099, A003313, A124677. %K A075100 hard,more,nonn %O A075100 1,3 %A A075100 _Colin Mallows_, Aug 31 2002 %E A075100 Edited by _Andrey Zabolotskiy_, Nov 08 2024